Slot antenna device

ABSTRACT

A slot antenna device includes: a first electrically conductive member having a first electrically conductive surface and a second electrically conductive surface; a second electrically conductive member having a third electrically conductive surface that opposes the second electrically conductive surface; a waveguide member on the second electrically conductive surface; and an artificial magnetic conductor extending on both sides of the waveguide member. The first electrically conductive member has a slot. The waveguide member an electrically-conductive waveguide that opposes the third electrically conductive surface. The waveguide member includes a first ridge and a second ridge. One end of the first ridge and one end of the second ridge are opposed to each other. As viewed from a direction perpendicular to the waveguide face, the slot is located between the one end of the first ridge and the one end of the second ridge.

BACKGROUND 1. Technical Field

The present disclosure relates to a slot antenna device.

2. Description of the Related Art

An antenna device in which one or more radiating elements (which mayhereinafter be also referred to as “antenna elements”) are arrayed on aline or a plane finds its use in various applications, e.g., radar andcommunication systems. In order to radiate electromagnetic waves from anantenna device, it is necessary to supply electromagnetic waves (e.g.,radio-frequency signal waves) to each antenna element, from a circuitwhich generates electromagnetic waves (“feed”). Such feeding ofelectromagnetic waves is performed via a waveguide. A waveguide is alsoused to send electromagnetic waves that are received at the antennaelements to a reception circuit.

Conventionally, feed to an array antenna has often been achieved byusing a microstrip line(s). However, in the case where the frequency ofan electromagnetic wave to be transmitted or received by an arrayantenna is a high frequency above 30 gigahertz (GHz), as in themillimeter band, a microstrip line will incur a large dielectric loss,thus detracting from the efficiency of the antenna. Therefore, in such aradio frequency region, an alternative waveguide to replace a microstripline is needed.

As alternative waveguide structures to the microstrip line, PatentDocuments 1 to 3, and Non-Patent Documents 1 and 2 disclose structureswhich guide electromagnetic waves by utilizing an artificial magneticconductor (AMC) extending on both sides of a ridge-type waveguide.Patent Document 1 and Non-Patent Document 1 disclose slot array antennasutilizing such a waveguide structure.

Patent Document 1: the specification of U.S. Pat. No. 8,779,995

Patent Document 2: the specification of U.S. Pat. No. 8,803,638

Patent Document 3: the specification of European Patent ApplicationPublication No. 1331688

Non-Patent Document 1: Kirino et al., “A 76 GHz Multi-Layered PhasedArray Antenna Using a Non-Metal Contact Metamaterial Waveguide”, IEEETransaction on Antennas and Propagation, Vol. 60, No. 2, February 2012,pp 840-853

Non-Patent Document 2: Kildal et al., “Local Metamaterial-BasedWaveguides in Gaps Between Parallel Metal Plates”, IEEE Antennas andWireless Propagation Letters, Vol. 8, 2009, pp 84-87

SUMMARY

The present disclosure provides an antenna device which is based on aprinciple which is different from conventional.

A slot antenna device according to one implementation of the presentdisclosure is a slot antenna device, including: a first electricallyconductive member having a first electrically conductive surface on afront side and a second electrically conductive surface on a rear side,and having at least one slot extending from the first electricallyconductive surface through to the second electrically conductivesurface; a second electrically conductive member on the rear side of thefirst electrically conductive member, the second electrically conductivemember having a third electrically conductive surface on the front side,the third electrically conductive surface opposing the secondelectrically conductive surface; a ridge-shaped waveguide member on thesecond electrically conductive surface of the first electricallyconductive member, the waveguide member having anelectrically-conductive waveguide face that opposes the thirdelectrically conductive surface and extending alongside the thirdelectrically conductive surface; and an artificial magnetic conductor onat least one of the second electrically conductive surface and the thirdelectrically conductive surface, the artificial magnetic conductorextending on both sides of the waveguide member. The third electricallyconductive surface, the waveguide face, and the artificial magneticconductor define a waveguide in a gap extending between the thirdelectrically conductive surface and the waveguide face. The waveguidemember includes a first ridge and a second ridge. One end of the firstridge and one end of the second ridge are opposed to each other. Asviewed from a direction perpendicular to the waveguide face, the slot islocated between the one end of the first ridge and the one end of thesecond ridge. The at least one slot is open to an external space throughthe first electrically conductive surface.

According to an embodiment of the present disclosure, a low-loss antennadevice can be realized based on a principle which is different fromconventional.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing a non-limitingexample of the fundamental construction of a waveguide device.

FIG. 2A is a diagram schematically showing a cross-sectionalconstruction of a waveguide device 100 as taken parallel to the XZplane.

FIG. 2B is a diagram schematically showing another cross-sectionalconstruction of the waveguide device 100 as taken parallel to the XZplane.

FIG. 3 is a perspective view schematically showing the waveguide device100, illustrated so that the spacing between a conductive member 110 anda conductive member 120 is exaggerated for ease of understanding.

FIG. 4 is a diagram showing an exemplary range of dimension of eachmember in the structure shown in FIG. 2A.

FIG. 5A is a diagram schematically showing an electromagnetic wave thatpropagates in a narrow space, i.e., a gap between a waveguide face 122 aof a waveguide member 122 and a conductive surface 110 a of a conductivemember 110.

FIG. 5B is a diagram schematically showing a cross section of a hollowwaveguide 130.

FIG. 5C is a cross-sectional view showing an implementation where twowaveguide members 122 are provided on the conductive member 120.

FIG. 5D is a diagram schematically showing a cross section of awaveguide device in which two hollow waveguides 130 are placedside-by-side.

FIG. 6A is a perspective view schematically showing a partialconstruction of a slot array antenna 200 (Comparative Example) utilizinga WRG structure.

FIG. 6B is a diagram schematically showing a partial cross section whichpasses through the centers of two slots 112 of a slot array antenna 200that are arranged along the X direction, the cross section being takenparallel to the XZ plane.

FIG. 7A is a perspective view schematically showing the construction ofan antenna device 300 according to an illustrative embodiment of thepresent disclosure.

FIG. 7B is a diagram schematically showing the positioning of a firstconductive member 110 and a waveguide member 122 and a plurality ofconductive rods 124 thereon.

FIG. 7C is a diagram schematically showing a cross section resulting bycutting the antenna device 300 shown in FIG. 7A at a plane which passesthrough the center of a slot 112 and is parallel to the XZ plane.

FIG. 7D is a diagram schematically showing a cross section resulting bycutting the antenna device 300 at a plane which passes through thecenter of a slot 112 and is parallel to the YZ plane.

FIG. 8A is a plan view schematically showing a partial construction ofan antenna device 300 according to a first embodiment of the presentdisclosure.

FIG. 8B is a perspective view showing more specifically the structure ofa first conductive member 110, and a waveguide member 122 thereon, ofthe antenna device 300.

FIG. 8C is a diagram schematically showing a cross-sectional structureof the antenna device 300 as taken on a cross section which passesthrough the centers of a plurality of slots 112 and is parallel to theYZ plane.

FIG. 8D is a perspective view showing one radiating element among theplurality of radiating elements in Embodiment 1.

FIG. 9A is a plan view showing a partial construction of an antennadevice 300 according to Embodiment 2.

FIG. 9B is a perspective view showing two radiating elements among fourradiating elements.

FIG. 10 a perspective view showing two radiating elements according to avariant of Embodiment 2.

FIG. 11A is a perspective view showing a radiating element according toanother variant of Embodiment 2.

FIG. 11B is a perspective view showing the interior of a radiatingelement according to another variant of Embodiment 2.

FIG. 12A is a diagram showing a first conductive member 110 of a slotantenna device 300 in which a plurality of horns 114 are providedrespectively around a plurality of H-shaped slots 112, as viewed fromthe rear side.

FIG. 12B is a cross-sectional view taken along line B-B in FIG. 12A.

FIG. 13A is a cross-sectional view schematically showing theconstruction of an antenna device 300 according to Embodiment 3.

FIG. 13B is a cross-sectional view showing a first variant of Embodiment3.

FIG. 13C is a cross-sectional view showing another variant of Embodiment3.

FIG. 14 is a perspective view showing a first conductive member 110 ofan exemplary antenna device 300 including a plurality of waveguidemembers 122.

FIG. 15 is a diagram for describing exemplary cross-sectional shapes ofa port 145 or slots 111, 112 more specifically.

FIG. 16A is a cross-sectional view showing an exemplary structure inwhich only a waveguide face 122 a, defining an upper face of thewaveguide member 122, is electrically conductive, while any portion ofthe waveguide member 122 other than the waveguide face 122 a is notelectrically conductive.

FIG. 16B is a diagram showing a variant in which the waveguide member122 is not formed on the conductive member 120.

FIG. 16C is a diagram showing an exemplary structure where theconductive member 120, the waveguide member 122, and each of theplurality of conductive rods 124 are composed of a dielectric surfacethat is coated with an electrically conductive material such as a metal.

FIG. 16D is a diagram showing an exemplary structure in which dielectriclayers 110 c and 120 c are respectively provided on the outermostsurfaces of conductive members 110 and 120, a waveguide member 122, andconductive rods 124.

FIG. 16E is a diagram showing another exemplary structure in whichdielectric layers 110 c and 120 c are respectively provided on theoutermost surfaces of conductive members 110 and 120, a waveguide member122, and conductive rods 124.

FIG. 16F is a diagram showing an example where the height of thewaveguide member 122 is lower than the height of the conductive rods124, and a portion of a conductive surface 110 a of the conductivemember 110 that opposes the waveguide face 122 a protrudes toward thewaveguide member 122.

FIG. 16G is a diagram showing an example where, further in the structureof FIG. 16F, portions of the conductive surface 110 a that oppose theconductive rods 124 protrude toward the conductive rods 124.

FIG. 17A is a diagram showing an example where a conductive surface 110a of the conductive member 110 is shaped as a curved surface.

FIG. 17B is a diagram showing an example where also a conductive surface120 a of the conductive member 120 is shaped as a curved surface.

FIG. 18 is a diagram showing a driver's vehicle 500, and a precedingvehicle 502 that is traveling in the same lane as the driver's vehicle500.

FIG. 19 is a diagram showing an onboard radar system 510 of the driver'svehicle 500.

FIG. 20A is a diagram showing a relationship between an array antenna AAof the onboard radar system 510 and plural arriving waves k.

FIG. 20B is a diagram showing the array antenna AA receiving the k^(th)arriving wave.

FIG. 21 is a block diagram showing an exemplary fundamental constructionof a vehicle travel controlling apparatus 600 according to the presentdisclosure.

FIG. 22 is a block diagram showing another exemplary construction forthe vehicle travel controlling apparatus 600.

FIG. 23 is a block diagram showing an example of a more specificconstruction of the vehicle travel controlling apparatus 600.

FIG. 24 is a block diagram showing a more detailed exemplaryconstruction of the radar system 510 according to this ApplicationExample.

FIG. 25 is a diagram showing change in frequency of a transmissionsignal which is modulated based on the signal that is generated by atriangular wave generation circuit 581.

FIG. 26 is a diagram showing a beat frequency fu in an “ascent” periodand a beat frequency fd in a “descent” period.

FIG. 27 is a diagram showing an exemplary implementation in which asignal processing circuit 560 is implemented in hardware including aprocessor PR and a memory device MD.

FIG. 28 is a diagram showing a relationship between three frequenciesf1, f2 and f3.

FIG. 29 is a diagram showing a relationship between synthetic spectra F1to F3 on a complex plane.

FIG. 30 is a flowchart showing the procedure of a process of determiningrelative velocity and distance.

FIG. 31 is a diagram concerning a fusion apparatus in which a radarsystem 510 having a slot array antenna and an onboard camera system 700are included.

FIG. 32 is a diagram illustrating how placing a millimeter wave radar510 and a camera at substantially the same position within the vehicleroom may allow them to acquire an identical field of view and line ofsight, thus facilitating a matching process.

FIG. 33 is a diagram showing an exemplary construction for a monitoringsystem 1500 based on millimeter wave radar.

FIG. 34 is a block diagram showing a construction for a digitalcommunication system 800A.

FIG. 35 is a block diagram showing an exemplary communication system800B including a transmitter 810B which is capable of changing its radiowave radiation pattern.

FIG. 36 is a block diagram showing an exemplary communication system800C implementing a MIMO function.

DETAILED DESCRIPTION

Prior to describing embodiments of the present disclosure, findings thatform the basis of the present disclosure will be described.

A ridge waveguide which is disclosed in the aforementioned PatentDocuments 1 to 3, and Non-Patent Documents 1 and 2 is provided in awaffle iron structure which is capable of functioning as an artificialmagnetic conductor. A ridge waveguide in which such an artificialmagnetic conductor is utilized based on the present disclosure (whichhereinafter may be referred to as a WRG: Waffle-iron Ridge waveguide) isable to realize an antenna feeding network with low losses in themicrowave or the millimeter wave band. Moreover, use of such a ridgewaveguide allows antenna elements to be disposed with a high density.Hereinafter, an exemplary fundamental construction and operation of sucha waveguide structure will be described.

An artificial magnetic conductor is a structure which artificiallyrealizes the properties of a perfect magnetic conductor (PMC), whichdoes not exist in nature. One property of a perfect magnetic conductoris that “a magnetic field on its surface has zero tangential component”.This property is the opposite of the property of a perfect electricconductor (PEC), i.e., “an electric field on its surface has zerotangential component”. Although no perfect magnetic conductor exists innature, it can be embodied by an artificial structure, e.g., an array ofa plurality of electrically conductive rods. An artificial magneticconductor functions as a perfect magnetic conductor in a specificfrequency band which is defined by its structure. An artificial magneticconductor restrains or prevents an electromagnetic wave of any frequencythat is contained in the specific frequency band (propagation-restrictedband) from propagating along the surface of the artificial magneticconductor. For this reason, the surface of an artificial magneticconductor may be referred to as a high impedance surface.

In the waveguide devices disclosed in Patent Documents 1 to 3 andNon-Patent Documents 1 and 2, an artificial magnetic conductor isrealized by a plurality of electrically conductive rods which arearrayed along row and column directions. Such rods are projections whichmay also be referred to as posts or pins. Each of these waveguidedevices includes, as a whole, a pair of opposing electrically conductiveplates. One conductive plate has a ridge protruding toward the otherconductive plate, and stretches of an artificial magnetic conductorextending on both sides of the ridge. An upper face (i.e., itselectrically conductive face) of the ridge opposes, via a gap, anelectrically conductive surface of the other conductive plate. Anelectromagnetic wave (signal wave) of a wavelength which is contained inthe propagation-restricted band of the artificial magnetic conductorpropagates along the ridge, in the space (gap) between this conductivesurface and the upper face of the ridge.

FIG. 1 is a perspective view schematically showing a non-limitingexample of a fundamental construction of such a waveguide device. FIG. 1shows XYZ coordinates along X, Y and Z directions which are orthogonalto one another. The waveguide device 100 shown in the figure includes aplate-like electrically conductive member 110 and a plate shape(plate-like) electrically conductive member 120, which are in opposingand parallel positions to each other. A plurality of electricallyconductive rods 124 are arrayed on the conductive member 120.

Note that any structure appearing in a figure of the present applicationis shown in an orientation that is selected for ease of explanation,which in no way should limit its orientation when an embodiment of thepresent disclosure is actually practiced. Moreover, the shape and sizeof a whole or a part of any structure that is shown in a figure shouldnot limit its actual shape and size.

FIG. 2A is a diagram schematically showing the construction of a crosssection of the waveguide device 100 in FIG. 1, taken parallel to the XZplane. As shown in FIG. 2A, the conductive member 110 has anelectrically conductive surface 110 a on the side facing the conductivemember 120. The conductive surface 110 a has a two-dimensional expansealong a plane which is orthogonal to the axial direction (i.e., the Zdirection) of the conductive rods 124 (i.e., a plane which is parallelto the XY plane). Although the conductive surface 110 a is shown to be asmooth plane in this example, the conductive surface 110 a does not needto be a plane, as will be described later.

FIG. 3 is a perspective view schematically showing the waveguide device100, illustrated so that the spacing between the conductive member 110and the conductive member 120 is exaggerated for ease of understanding.In an actual waveguide device 100, as shown in FIG. 1 and FIG. 2A, thespacing between the conductive member 110 and the conductive member 120is narrow, with the conductive member 110 covering over all of theconductive rods 124 on the conductive member 120.

FIG. 1 to FIG. 3 only show portions of the waveguide device 100. Theconductive members 110 and 120, the waveguide member 122, and theplurality of conductive rods 124 actually extend to outside of theportions illustrated in the figures. At an end of the waveguide member122, as will be described later, a choke structure for preventingelectromagnetic waves from leaking into the external space is provided.The choke structure may include a row of conductive rods that areadjacent to the end of the waveguide member 122, for example.

See FIG. 2A again. The plurality of conductive rods 124 arrayed on theconductive member 120 each have a leading end 124 a opposing theconductive surface 110 a. In the example shown in the figure, theleading ends 124 a of the plurality of conductive rods 124 are on thesame plane. This plane defines the surface 125 of an artificial magneticconductor. Each conductive rod 124 does not need to be entirelyelectrically conductive, so long as it at least includes an electricallyconductive layer that extends along the upper face and the side face ofthe rod-like structure. Although this electrically conductive layer maybe located at the surface layer of the rod-like structure, the surfacelayer may be composed of an insulation coating or a resin layer with noelectrically conductive layer existing on the surface of the rod-likestructure. Moreover, each conductive member 120 does not need to beentirely electrically conductive, so long as it can support theplurality of conductive rods 124 to constitute an artificial magneticconductor. Of the surfaces of the conductive member 120, a face 120 acarrying the plurality of conductive rods 124 may be electricallyconductive, such that the electrical conductor electricallyinterconnects the surfaces of adjacent ones of the plurality ofconductive rods 124. Moreover, the electrically conductive layer of thesecond conductive member 120 may be covered with an insulation coatingor a resin layer. In other words, the entire combination of theconductive member 120 and the plurality of conductive rods 124 may atleast include an electrically conductive layer with rises and fallsopposing the conductive surface 110 a of the conductive member 110.

On the conductive member 120, a ridge-like waveguide member 122 isprovided among the plurality of conductive rods 124. More specifically,stretches of an artificial magnetic conductor are present on both sidesof the waveguide member 122, such that the waveguide member 122 issandwiched between the stretches of artificial magnetic conductor onboth sides. As can be seen from FIG. 3, the waveguide member 122 in thisexample is supported on the conductive member 120, and extends linearlyalong the Y direction. In the example shown in the figure, the waveguidemember 122 has the same height and width as those of the conductive rods124. As will be described later, however, the height and width of thewaveguide member 122 may have different values from those of theconductive rod 124. Unlike the conductive rods 124, the waveguide member122 extends along a direction (which in this example is the Y direction)in which to guide electromagnetic waves along the conductive surface 110a. Similarly, the waveguide member 122 does not need to be entirelyelectrically conductive, but may at least include an electricallyconductive waveguide face 122 a opposing the conductive surface 110 a ofthe conductive member 110. The conductive member 120, the plurality ofconductive rods 124, and the waveguide member 122 may be portions of acontinuous single-piece body. Furthermore, the conductive member 110 mayalso be a portion of such a single-piece body.

On both sides of the waveguide member 122, the space between the surface125 of each stretch of artificial magnetic conductor and the conductivesurface 110 a of the conductive member 110 does not allow anelectromagnetic wave of any frequency that is within a specificfrequency band to propagate. This frequency band is called a “prohibitedband”. The artificial magnetic conductor is designed so that thefrequency of an electromagnetic wave (signal wave) to propagate in thewaveguide device 100 (which may hereinafter be referred to as the“operating frequency”) is contained in the prohibited band. Theprohibited band may be adjusted based on the following: the height ofthe conductive rods 124, i.e., the depth of each groove formed betweenadjacent conductive rods 124; the width of each conductive rod 124; theinterval between conductive rods 124; and the size of the gap betweenthe leading end 124 a and the conductive surface 110 a of eachconductive rod 124.

Next, with reference to FIG. 4, the dimensions, shape, positioning, andthe like of each member will be described.

FIG. 4 is a diagram showing an exemplary range of dimension of eachmember in the structure shown in FIG. 2A. The waveguide device is usedfor at least one of transmission and reception of electromagnetic wavesof a predetermined band (referred to as the “operating frequency band”).In the present specification, λo denotes a representative value ofwavelengths in free space (e.g., a central wavelength corresponding to acenter frequency in the operating frequency band) of an electromagneticwave (signal wave) propagating in a waveguide extending between theconductive surface 110 a of the conductive member 110 and the waveguideface 122 a of the waveguide member 122. Moreover, λm denotes awavelength, in free space, of an electromagnetic wave of the highestfrequency in the operating frequency band. The end of each conductiverod 124 that is in contact with the conductive member 120 is referred toas the “root”. As shown in FIG. 4, each conductive rod 124 has theleading end 124 a and the root 124 b. Examples of dimensions, shapes,positioning, and the like of the respective members are as follows.

(1) Width of the Conductive Rod

The width (i.e., the size along the X direction and the Y direction) ofthe conductive rod 124 may be set to less than λm/2. Within this range,resonance of the lowest order can be prevented from occurring along theX direction and the Y direction. Since resonance may possibly occur notonly in the X and Y directions but also in any diagonal direction in anX-Y cross section, the diagonal length of an X-Y cross section of theconductive rod 124 is also preferably less than λm/2. The lower limitvalues for the rod width and diagonal length will conform to the minimumlengths that are producible under the given manufacturing method, but isnot particularly limited.

(2) Distance from the Root of the Conductive Rod to the ConductiveSurface of the Conductive Member

The distance from the root 124 b of each conductive rod 124 to theconductive surface 110 a of the conductive member 110 may be longer thanthe height of the conductive rods 124, while also being less than λm/2.When the distance is λm/2 or more, resonance may occur between the root124 b of each conductive rod 124 and the conductive surface 110 a, thusreducing the effect of signal wave containment.

The distance from the root 124 b of each conductive rod 124 to theconductive surface 110 a of the conductive member 110 corresponds to thespacing between the conductive member 110 and the conductive member 120.For example, when a signal wave of 76.5±0.5 GHz (which belongs to themillimeter band or the extremely high frequency band) propagates in thewaveguide, the wavelength of the signal wave is in the range from 3.8934mm to 3.9446 mm. Therefore, λm equals 3.8934 mm in this case, so thatthe spacing between the conductive member 110 and the conductive member120 may be set to less than a half of 3.8934 mm. So long as theconductive member 110 and the conductive member 120 realize such anarrow spacing while being disposed opposite from each other, theconductive member 110 and the conductive member 120 do not need to bestrictly parallel. Moreover, when the spacing between the conductivemember 110 and the conductive member 120 is less than λm/2, a whole or apart of the conductive member 110 and/or the conductive member 120 maybe shaped as a curved surface. On the other hand, the conductive members110 and 120 each have a planar shape (i.e., the shape of their region asperpendicularly projected onto the XY plane) and a planar size (i.e.,the size of their region as perpendicularly projected onto the XY plane)which may be arbitrarily designed depending on the purpose.

Although the conductive surface 120 a is illustrated as a plane in theexample shown in FIG. 2A, embodiments of the present disclosure are notlimited thereto. For example, as shown in FIG. 2B, the conductivesurface 120 a may be the bottom parts of faces each of which has a crosssection similar to a U-shape or a V-shape. The conductive surface 120 awill have such a structure when each conductive rod 124 or the waveguidemember 122 is shaped with a width which increases toward the root. Evenwith such a structure, the device shown in FIG. 2B can function as thewaveguide device according to an embodiment of the present disclosure solong as the distance between the conductive surface 110 a and theconductive surface 120 a is less than a half of the wavelength λm.

(3) Distance L2 from the Leading End of the Conductive Rod to theConductive Surface

The distance L2 from the leading end 124 a of each conductive rod 124 tothe conductive surface 110 a is set to less than λm/2. When the distanceis λm/2 or more, a propagation mode where electromagnetic wavesreciprocate between the leading end 124 a of each conductive rod 124 andthe conductive surface 110 a may occur, thus no longer being able tocontain an electromagnetic wave. Note that, among the plurality ofconductive rods 124, at least those which are adjacent to the waveguidemember 122 do not have their leading ends in electrical contact with theconductive surface 110 a. As used herein, the leading end of aconductive rod not being in electrical contact with the conductivesurface means either of the following states: there being an air gapbetween the leading end and the conductive surface; or the leading endof the conductive rod and the conductive surface adjoining each othervia an insulating layer which may exist in the leading end of theconductive rod or in the conductive surface.

(4) Arrangement and Shape of Conductive Rods

The interspace between two adjacent conductive rods 124 among theplurality of conductive rods 124 has a width of less than λm/2, forexample. The width of the interspace between any two adjacent conductiverods 124 is defined by the shortest distance from the surface (sideface) of one of the two conductive rods 124 to the surface (side face)of the other. This width of the interspace between rods is to bedetermined so that resonance of the lowest order will not occur in theregions between rods. The conditions under which resonance will occurare determined based by a combination of: the height of the conductiverods 124; the distance between any two adjacent conductive rods; and thecapacitance of the air gap between the leading end 124 a of eachconductive rod 124 and the conductive surface 110 a. Therefore, thewidth of the interspace between rods may be appropriately determineddepending on other design parameters. Although there is no clear lowerlimit to the width of the interspace between rods, for manufacturingease, it may be e.g. λm/16 or more when an electromagnetic wave in theextremely high frequency range is to be propagated. Note that theinterspace does not need to have a constant width. So long as it remainsless than λm/2, the interspace between conductive rods 124 may vary.

The arrangement of the plurality of conductive rods 124 is not limitedto the illustrated example, so long as it exhibits a function of anartificial magnetic conductor. The plurality of conductive rods 124 donot need to be arranged in orthogonal rows and columns; the rows andcolumns may be intersecting at angles other than 90 degrees. Theplurality of conductive rods 124 do not need to form a linear arrayalong rows or columns, but may be in a dispersed arrangement which doesnot present any straightforward regularity. The conductive rods 124 mayalso vary in shape and size depending on the position on the conductivemember 120.

The surface 125 of the artificial magnetic conductor that areconstituted by the leading ends 124 a of the plurality of conductiverods 124 does not need to be a strict plane, but may be a plane withminute rises and falls, or even a curved surface. In other words, theconductive rods 124 do not need to be of uniform height, but rather theconductive rods 124 may be diverse so long as the array of conductiverods 124 is able to function as an artificial magnetic conductor.

Each conductive rod 124 does not need to have a prismatic shape as shownin the figure, but may have a cylindrical shape, for example.Furthermore, each conductive rod 124 does not need to have a simplecolumnar shape. The artificial magnetic conductor may also be realizedby any structure other than an array of conductive rods 124, and variousartificial magnetic conductors are applicable to the waveguide device ofthe present disclosure. Note that, when the leading end 124 a of eachconductive rod 124 has a prismatic shape, its diagonal length ispreferably less than λm/2. When the leading end 124 a of each conductiverod 124 is shaped as an ellipse, the length of its major axis ispreferably less than λm/2. Even when the leading end 124 a has any othershape, the dimension across it is preferably less than λm/2 even at thelongest position.

The height of each conductive rod 124 (in particular, those conductiverods 124 which are adjacent to the waveguide member 122), i.e., thelength from the root 124 b to the leading end 124 a, may be set to avalue which is shorter than the distance (i.e., less than λm/2) betweenthe conductive surface 110 a and the conductive surface 120 a, e.g.,λo/4.

(5) Width of the Waveguide Face

The width of the waveguide face 122 a of the waveguide member 122, i.e.,the size of the waveguide face 122 a along a direction which isorthogonal to the direction that the waveguide member 122 extends, maybe set to less than λm/2 (e.g. λo/8). If the width of the waveguide face122 a is λm/2 or more, resonance will occur along the width direction,which will prevent any WRG from operating as a simple transmission line.

(6) Height of the Waveguide Member

The height (i.e., the size along the Z direction in the example shown inthe figure) of the waveguide member 122 is set to less than λm/2. Thereason is that, if the distance is λm/2 or more, the distance betweenthe root 124 b of each conductive rod 124 and the conductive surface 110a will be λm/2 or more. Similarly, the height of the conductive rods 124(in particular, those conductive rods 124 which are adjacent to thewaveguide member 122) is also set to less than λm/2.

(7) Distance L1 between the Waveguide Face and the Conductive Surface

The distance L1 between the waveguide face 122 a of the waveguide member122 and the conductive surface 110 a is set to less than λm/2. If thedistance is λm/2 or more, resonance will occur between the waveguideface 122 a and the conductive surface 110 a, which will preventfunctionality as a waveguide. In one example, the distance L1 is λm/4 orless. In order to ensure manufacturing ease, when an electromagneticwave in the extremely high frequency range is to propagate, the distanceL1 is preferably λm/16 or more, for example.

The lower limit of the distance L1 between the conductive surface 110 aand the waveguide face 122 a and the lower limit of the distance L2between the conductive surface 110 a and the leading end 124 a of eachconductive rod 124 depends on the machining precision, and also on theprecision when assembling the two upper/lower conductive members 110 and120 so as to be apart by a constant distance. When a pressing techniqueor an injection technique is used, the practical lower limit of theaforementioned distance is about 50 micrometers (μm). In the case ofusing an MEMS (Micro-Electro-Mechanical System) technique to make aproduct in e.g. the terahertz range, the lower limit of theaforementioned distance is about 2 to about 3 μm.

In the waveguide device 100 of the above-described construction, asignal wave of the operating frequency is unable to propagate in thespace between the surface 125 of the artificial magnetic conductor andthe conductive surface 110 a of the conductive member 110, butpropagates in the space between the waveguide face 122 a of thewaveguide member 122 and the conductive surface 110 a of the conductivemember 110. Unlike in a hollow waveguide, the width of the waveguidemember 122 in such a waveguide structure does not need to be equal to orgreater than a half of the wavelength of the electromagnetic wave topropagate. Moreover, the conductive member 110 and the conductive member120 do not need to be interconnected by a metal wall that extends alongthe thickness direction (i.e., in parallel to the YZ plane).

FIG. 5A schematically shows an electromagnetic wave that propagates in anarrow space, i.e., a gap between the waveguide face 122 a of thewaveguide member 122 and the conductive surface 110 a of the conductivemember 110. Three arrows in FIG. 5A schematically indicate theorientation of an electric field of the propagating electromagneticwave. The electric field of the propagating electromagnetic wave isperpendicular to the conductive surface 110 a of the conductive member110 and to the waveguide face 122 a.

On both sides of the waveguide member 122, stretches of artificialmagnetic conductor that are created by the plurality of conductive rods124 are present. An electromagnetic wave propagates in the gap betweenthe waveguide face 122 a of the waveguide member 122 and the conductivesurface 110 a of the conductive member 110. FIG. 5A is schematic, anddoes not accurately represent the magnitude of an electromagnetic fieldto be actually created by the electromagnetic wave. A part of theelectromagnetic wave (electromagnetic field) propagating in the spaceover the waveguide face 122 a may have a lateral expanse, to the outside(i.e., toward where the artificial magnetic conductor exists) of thespace that is delineated by the width of the waveguide face 122 a. Inthis example, the electromagnetic wave propagates in a direction (i.e.,the Y direction) which is perpendicular to the plane of FIG. 5A. Assuch, the waveguide member 122 does not need to extend linearly alongthe Y direction, but may include a bend(s) and/or a branching portion(s)not shown. Since the electromagnetic wave propagates along the waveguideface 122 a of the waveguide member 122, the direction of propagationwould change at a bend, whereas the direction of propagation wouldramify into plural directions at a branching portion.

In the waveguide structure of FIG. 5A, no metal wall (electric wall),which would be indispensable to a hollow waveguide, exists on both sidesof the propagating electromagnetic wave. Therefore, in the waveguidestructure of this example, “a constraint due to a metal wall (electricwall)” is not included in the boundary conditions for theelectromagnetic field mode to be created by the propagatingelectromagnetic wave, and the width (size along the X direction) of thewaveguide face 122 a is less than a half of the wavelength of theelectromagnetic wave.

For reference, FIG. 5B schematically shows a cross section of a hollowwaveguide 130. With arrows, FIG. 5B schematically shows the orientationof an electric field of an electromagnetic field mode (TE₁₀) that iscreated in the internal space 132 of the hollow waveguide 130. Thelengths of the arrows correspond to electric field intensities. Thewidth of the internal space 132 of the hollow waveguide 130 needs to beset to be broader than a half of the wavelength. In other words, thewidth of the internal space 132 of the hollow waveguide 130 cannot beset to be smaller than a half of the wavelength of the propagatingelectromagnetic wave.

FIG. 5C is a cross-sectional view showing an implementation where twowaveguide members 122 are provided on the conductive member 120. Thus,an artificial magnetic conductor that is created by the plurality ofconductive rods 124 exists between the two adjacent waveguide members122. More accurately, stretches of artificial magnetic conductor createdby the plurality of conductive rods 124 are present on both sides ofeach waveguide member 122, such that each waveguide member 122 is ableto independently propagate an electromagnetic wave.

For reference's sake, FIG. 5D schematically shows a cross section of awaveguide device in which two hollow waveguides 130 are placedside-by-side. The two hollow waveguides 130 are electrically insulatedfrom each other. Each space in which an electromagnetic wave is topropagate needs to be surrounded by a metal wall that defines therespective hollow waveguide 130. Therefore, the interval between theinternal spaces 132 in which electromagnetic waves are to propagatecannot be made smaller than a total of the thicknesses of two metalwalls. Usually, a total of the thicknesses of two metal walls is longerthan a half of the wavelength of a propagating electromagnetic wave.Therefore, it is difficult for the interval between the hollowwaveguides 130 (i.e., interval between their centers) to be shorter thanthe wavelength of a propagating electromagnetic wave. Particularly forelectromagnetic waves of wavelengths in the extremely high frequencyrange (i.e., electromagnetic wave wavelength: 10 mm or less) or evenshorter wavelengths, a metal wall which is sufficiently thin relative tothe wavelength is difficult to be formed. This presents a cost problemin commercially practical implementation.

On the other hand, a waveguide device 100 including an artificialmagnetic conductor can easily realize a structure in which waveguidemembers 122 are placed close to one another. Thus, such a waveguidedevice 100 can be suitably used in an array antenna that includes pluralantenna elements in a close arrangement.

FIG. 6A is a perspective view schematically showing an exemplaryconstruction of a slot array antenna 200 (Comparative Example) utilizingthe above-described waveguide structure. FIG. 6B is a diagramschematically showing a partial cross section which passes through thecenters of two slots 112 of a slot array antenna 200 that are arrangedalong the X direction, the cross section being taken parallel to the XZplane. In the slot array antenna 200, the first conductive member 110includes a plurality of slots 112 that are arrayed along the X directionand the Y direction. In this example, the plurality of slots 112 includetwo slot rows. Each slot row includes six slots 112 that are arrangedalong the Y direction at equal intervals. On the second conductivemember 120, two waveguide members 122 that extend along the Y directionare provided. Each waveguide member 122 has an electrically-conductivewaveguide face 122 a opposing one slot row. In the region between thetwo waveguide members 122 and in the regions outside the two waveguidemembers 122, a plurality of conductive rods 124 are provided. Theconductive rods 124 constitute an artificial magnetic conductor.

To the waveguide extending between the waveguide face 122 a of eachwaveguide member 122 and the conductive surface 110 a of the conductivemember 110, an electromagnetic wave is supplied from a transmissioncircuit not shown. Among the plurality of slot 112 arranged along the Ydirection, the distance between the centers of every two adjacent slots112 is designed so as to have the same value as the wavelength of anelectromagnetic wave propagating in the waveguide, for example. As aresult, electromagnetic waves with an equal phase will be radiated fromthe six slots 112 that are arranged along the Y direction.

The slot array antenna 200 shown in FIG. 6A and FIG. 6B is an antennaarray whose radiating elements are the plurality of slots 112. With thisconstruction of the slot array antenna 200, the interval between thecenters of radiating elements along the X direction can be made shorterthan the wavelength λ0 in free space of an electromagnetic wavepropagating in the waveguide, for example.

The inventors have found that an antenna device with low loss can berealized by a structure which is distinct from that of the slot arrayantenna 200 as described above. Hereinafter, an exemplary fundamentalconstruction of an embodiment of the present disclosure will bedescribed.

First, with reference to FIGS. 7A through 7D, the construction of a slotantenna device 300 (which hereinafter may simply be referred to as an“antenna device 300”) according to an illustrative embodiment of thepresent disclosure will be described. In the present disclosure, forconvenience, “the front side” refers to the side that borders on thefree space in which an electromagnetic wave radiated from the antennadevice 300 or an electromagnetic wave incident to the antenna device 300is to propagate; the opposite side is referred to as “the rear side”. Inthe present disclosure, terms such as “first”, “second”, etc., areemployed only for the sake of distinction between members, devices,parts, portions, layers, regions, or the like, without bearing anylimitations in meaning.

FIG. 7A is a perspective view schematically showing the construction ofthe antenna device 300 according to an illustrative embodiment of thepresent disclosure. The antenna device 300 includes a first conductivemember 110 and a second conductive member 120 that are opposed to eachother. The first conductive member 110 has a slot 112. In thisembodiment, unlike in Comparative Example described above, a waveguidemember 122 and a plurality of conductive rods 124 are connected to thefirst conductive member 110, rather than to the second conductive member120.

FIG. 7B schematically shows positioning of the first conductive member110, and the waveguide member 122 and the plurality of conductive rods124 thereon. The waveguide member 122, which is a ridge-shaped memberbeing provided on the first conductive member 110 and having anelectrically-conductive surface, is split into a first ridge 122A and asecond ridge 122B at the position of the slot 112.

FIG. 7C is a diagram schematically showing a cross section resulting bycutting the antenna device 300 shown in FIG. 7A at a plane which passesthrough the center of the slot 112 and is parallel to the XZ plane. FIG.7D is a diagram schematically showing a cross section resulting bycutting the antenna device 300 at a plane which passes through thecenter of the slot 112 and is parallel to the YZ plane.

The first conductive member 110 has a first conductive surface 110 b onthe front side and a second conductive surface 110 a on the rear side.The first conductive member 110 has at least one slot 112 which extendsfrom the first conductive surface 110 b through to the second conductivesurface 110 a. Although the first conductive member 110 in this exampleis illustrated as having one slot 112, the first conductive member 110may have a plurality of slots 112, as is the case with ComparativeExample described above.

The second conductive member 120 is on the rear side of the firstconductive member 110. The second conductive member 120 has a thirdconductive surface 120 a on the front side, the third conductive surface120 a opposing the second conductive surface 110 a.

As shown in FIG. 7D, the waveguide member 122 is on the secondconductive surface 110 a of the first conductive member 110, and has aridge shape. The waveguide member 122 has an electrically-conductivewaveguide face 122 a opposing the third conductive surface 120 a of thesecond conductive member 120. The waveguide member 122 extends alongsidethe third conductive surface 120 a. The waveguide face 122 a of thewaveguide member 122 has a stripe shape (which may also be referred toas a “strip shape”) that extends alongside the third conductive surface120 a.

In the present specification, a “stripe shape” means a shape which isdefined by a single stripe, rather than a shape constituted by stripes.Not only shapes that extend linearly in one direction, but also anyshape that bends or branches along the way is also encompassed by a“stripe shape”. The shape falls under the meaning of “stripe shape” solong as it includes a portion that extends in one direction as viewedfrom the normal direction of the waveguide face 122 a.

The artificial magnetic conductor in the present embodiment includes theplurality of conductive rods 124. The artificial magnetic conductorextends on both sides of the waveguide member 122, and suppressesleakage of an electromagnetic wave that propagates along the waveguidemember 122. As shown in FIG. 7C, the artificial magnetic conductor isdisposed on the second conductive surface 110 a. Without being limitedto this example, the artificial magnetic conductor may be disposed onthe third conductive surface 120 a. The artificial magnetic conductormay exist on at least one of the second conductive surface 110 a and thethird conductive surface 120 a.

The third conductive surface 120 a, the waveguide face 122 a, and theartificial magnetic conductor define a waveguide, in a gap extendingbetween the third conductive surface 120 a and the waveguide face 122 a.This waveguide is connected to the external space via the slot 112. Inother words, the slot 112 is open to the external space.

As shown in FIGS. 7B and 7D, the waveguide member 122 includes the firstridge 122A and the second ridge 122B, which extend along a common path.To “extend along a path” means extending along an imaginary path, andmay encompass not only extending along a straight line, but alsoextending along a curve or a bent line. One end of the first ridge 122Aand one end of the second ridge 122B are opposed to each other. One endsof two ridges being opposed to each other means that these end faces ofthe ridges are disposed so as to face each other.

As viewed from a direction perpendicular to the waveguide face 122 a,the slot 112 is located between one end of the first ridge 122A and oneend of the second ridge 122B. In the example shown in FIG. 7D, the endfaces 122 c of the first ridge 122A and the second ridge 122B thatoppose each other are continuous with an inner wall surface 112 c of theslot 112. In the example shown in FIG. 7D, the inner wall surface of theslot 112 and the end faces 122 c of the ridges 122A and 122B are notshown to be stepped where they are continuously connected; however, theymay alternatively be stepped.

The size of the gap between the end face 122 c of the first ridge 122Aand the end face 122 c of the second ridge 122B may vary along adirection perpendicular to the waveguide face (i.e., the Z direction).For example, in order to suppress reflection of signal waves, the sizeof the gap between the first ridge 122A and the second ridge 122B may belocally adjusted. The size of the gap between the two end faces 122 c isdesigned so that the waveguide extending between the waveguide face 122a and the third conductive surface 120 a couples with the external spacevia the gap between the two end faces 122 c and the interior of the slot112.

The waveguide extending between the waveguide face 122 a of the firstridge 122A and the third conductive surface 120 a, or the waveguideextending between the waveguide face 122 a of the second ridge 122B andthe third conductive surface 120 a, is to be connected to a transmitteror receiver not shown in use. During transmission, an electromagneticwave which is supplied from the transmitter propagates in the waveguide,and passes between the two end faces 122 c of the ridges 122A and 122Band through the interior of the slot 112, so as to be radiated to theexternal space. During reception, an electromagnetic wave which impingeson the slot 112 from the external space passes through the interior ofthe slot 112 and between the end faces 122 c of the ridges 122A and122B, and propagates along the ridge 122A or 122B, so as to be receivedby the reception circuit.

Thus, the structure shown in FIG. 7D functions as an antenna element foruse in at least one of transmission and reception. Since the waveguidemember 122 and the slot 112 are both provided on the first conductivemember 110, the structure of the second conductive member 120 can besimplified.

Although the above example illustrates that the first conductive member110 has one slot 112, the first conductive member 110 may have aplurality of slots 112. By constructing a one-dimensional ortwo-dimensional array of plural slots 112, it becomes possible to createa low-loss antenna array.

Hereinafter, more specific exemplary constructions for waveguide deviceaccording to embodiments of the present disclosure will be described.Note however that unnecessarily detailed descriptions may be omitted.For example, detailed descriptions on what is well known in the art orredundant descriptions on what is substantially the same constitutionmay be omitted. This is to avoid lengthy description, and facilitate theunderstanding of those skilled in the art. The accompanying drawings andthe following description, which are provided by the inventors so thatthose skilled in the art can sufficiently understand the presentdisclosure, are not intended to limit the scope of claims. In thepresent specification, identical or similar constituent elements aredenoted by identical reference numerals.

Embodiment 1

FIG. 8A is a plan view schematically showing a partial construction of aslot antenna device 300 according to a first embodiment of the presentdisclosure. FIG. 8B is a perspective view showing more specifically thestructure of a first conductive member 110, and a waveguide member 122thereon, of the antenna device 300. In FIG. 8B, a plurality ofconductive rods 124 are shown with thin-colored lines except for a few.FIG. 8C is a diagram schematically showing a cross-sectional structureof the antenna device 300 as taken on a cross section which passesthrough the centers of a plurality of slots 112 and is parallel to theYZ plane.

The antenna device 300 of the present embodiment has a slot antennaarray structure whose radiating elements are a plurality of slots 112.The first conductive member 110 has the plurality of slots 112. Theplurality of slots 112 are arrayed along the Y direction, in which thewaveguide member 122 extends. The plurality of slots 112 include fourslots 112A, 112B, 112C and 112D.

The waveguide member 122 is split into a plurality of portions at thepositions of the plurality of slots 112. In the present specification,these split portions are each referred to as a “ridge”. The waveguidemember 122 in the present embodiment includes five ridges 122Ch, 122A,122B, 122C and 122D that are on a straight line. As viewed from adirection perpendicular to the waveguide face of the waveguide member122, each slot 112 is located between ends of two adjacent ones of theplurality of ridges. Specifically, the slot 112A is located between theridge 122Ch and the ridge 122A. The slot 112B is located between theridge 122A and the ridge 122B. The slot 112C is located between theridge 122B and the ridge 122C. The slot 112D is located between theridge 122C and the ridge 122D.

In the present specification, without distinction, the slots 112A, 112B,112C and 112D may collectively be represented as “slots 112”. Similarly,without distinction, the ridges 122Ch, 122A, 122B, 122C and 122D maycollectively be represented as “ridges 122”. The same is true of anyother constituent element.

Adjacent to the endmost slot 112A among the plurality of slots 112, achoke structure 150 is provided. The choke structure 150 may be composedof, for example: an additional transmission line having a length ofapproximately λ0/8; and a row of plural grooves of having a depth ofapproximately λ0/4, or a row of plural conductive rods 124 having aheight of approximately λ0/4, that are disposed at an end of theadditional transmission line. In the present embodiment, the chokestructure 150 includes the ridge 122Ch and one or more conductive rods124 that are closely located to the ridge 122Ch along the Y direction.In this case, the additional transmission line corresponds to thewaveguide extending between the ridge 122Ch and the third conductivesurface 120 a. In the following description, the ridge which is includedin the choke structure 150 will be referred to as a “choke ridge”.

The choke structure 150 confers a phase difference of about 180° (π)between an incident wave and a reflected wave, thereby restrainingelectromagnetic waves from leaking at the end of the waveguide member122. Rather than on the first conductive member 110, such a chokestructure 150 may be provided on the second conductive member 120.

Conventionally it has been believed that the length of the additionaltransmission line of a choke structure should be λr/4. Herein, λr is thewavelength of a signal wave on the transmission line. However, theinventors have found that, even when the length of the additionaltransmission line of the choke structure is shorter than λr/4, leakageof electromagnetic waves can still be suppressed, and an actually betterfunctionality than in the case of λr/4 may be obtained. In actuality,the length of the additional transmission line is preferably λ0/4 orless, i.e., shorter than λr/4. In the present embodiment, the length ofthe additional transmission line, i.e., the length of the choke ridge122Ch along the Y direction, is set to be equal to or greater than λ0/16and less than λ0/4, for example.

The conductive rods 124 included in the choke structure 150 may have adifferent shape from that of the conductive rods 124 which are includedin the artificial magnetic conductor extending on both sides of thewaveguide member 122. The choke ridge 122Ch may have the same shape asthe conductive rod 124.

In the present embodiment, the artificial magnetic conductor extendingon both sides of the waveguide member 122 includes a row of conductiverods 124 that lie adjacent to the waveguide member 122 in the +Xdirection and a row of conductive rods 124 that lie adjacent to thewaveguide member 122 in the −X direction. In each such row of conductiverods 124, the plurality of conductive rods 124 are arranged along the Ydirection. The artificial magnetic conductor on one side of thewaveguide member 122 may include two or more rows of conductive rods124. As will be described later, in the present disclosure, even asingle row of conductive rods 124 is to be regarded as an artificialmagnetic conductor.

As shown in FIG. 8C, the waveguide extending between the waveguidemember 122 and the second conductive member 120 is connected to atransmitter or a receiver, either directly or via another waveguide. Theother waveguide may include another ridge waveguide not shown, hollowwaveguide, or microstrip line, for example. The transmitter or receivermay be provided in a different layer from the layer in which thewaveguide shown in FIG. 8C is formed. In that case, a waveguide thatconnects between such layers is to be employed.

The transmitter is a device or circuit which feeds power to thewaveguide in the antenna device 300 and causes a signal wave to beradiated from each slot 112. The receiver is a device or circuit whichreceives a signal wave that has impinged on each slot 112 of the antennadevice 300 and propagated through the waveguide. Each of the transmitterand the receiver may be implemented as a millimeter wave integratedcircuit, for example. The antenna device 300 may be connected to adevice that functions both as a transmitter and as a receiver.

During transmission, a signal wave which is supplied from thetransmitter propagates through the waveguide extending between thewaveguide member 122 and the second conductive member 120 and excitesthe plurality of slots 112. As a result, signal waves are radiated.Conversely, during reception, signal waves impinging on the plurality ofslots 112 propagate through the waveguide extending between thewaveguide member 122 and the second conductive member 120 and arrive atthe receiver. As a result, signal waves are received.

The intervals between the plurality of slots 112 is set to beapproximately equal to the wavelength of a signal wave propagating inthe waveguide, for example. In that case, signal waves with an equalphase are radiated from the respective slots 112. For other purposes,e.g., reducing side lobes, etc., the intervals between slots 112 may bedifferent from the wavelength of a signal wave in the waveguide.

FIG. 8D is a perspective view showing one radiating element among theplurality of radiating elements in the present embodiment. In FIG. 8D,the plurality of conductive rods 124 and the second conductive member120 are omitted from illustration.

According to the present embodiment, a cross section of each slot 112that is perpendicular to its center axis has an H shape. The center axisof a slot 112 is defined as an axis which passes through the center ofthe slot 112 and is perpendicular to the apertured plane of the slot112. An “H shape” is meant to be a shape which, like the alphabeticalletter “H”, includes two vertical portions that are substantiallyparallel to each other and a lateral portion that connects between thecentral portions of the two vertical portions. Using an H-shaped slot112 allows the width along a direction perpendicular to the E plane tobe reduced as compared to the shape of the slot 112 shown in FIG. 7A.Note that the E plane is a plane that contains electric field vectors tobe created in the central portion of a slot 112. In the examples of FIG.7A and FIG. 8A, the E plane is parallel to the YZ plane.

With the above construction, a slot antenna device for transmissionpurposes or for reception purposes is realized whose radiating elementsare the plurality of slots 112. Since a WRG structure is utilized as inComparative Example, a low-loss antenna can be realized even in thehigh-frequency regions, as compared to an antenna utilizing microstriplines.

Embodiment 2

Next, a second embodiment of the present disclosure will be described.

FIG. 9A is a plan view showing a partial construction of a slot antennadevice 300 according to the present embodiment. A difference between thepresent embodiment and Embodiment 1 is that the shape of the opening ofeach slot 112 is an I shape. An “I shape” is meant to be a shape which,like the alphabetical letter “I”, extends in the manner of a straightline. Otherwise, the present embodiment is similar to Embodiment 1.

FIG. 9B is a perspective view showing two radiating elements among fourradiating elements. In FIG. 9B, the plurality of conductive rods 124 areomitted from illustration. Even when I-shaped slots 112 are used asradiating elements, an efficient slot antenna can be realized, similarlyto Embodiment 1.

The first conductive surface 110 b of the first conductive member 110may have a shape that defines at least one horn which communicates withat least one slot 112. By providing such a horn(s), the degree ofimpedance matching is increased, whereby signal wave reflection can besuppressed.

FIG. 10 is a perspective view showing two radiating elements accordingto a variant of Embodiment 2. In FIG. 10, the plurality of conductiverods 124 and the second conductive member 120 are omitted fromillustration. In this variant, the first conductive surface 110 b of thefirst conductive member 110 on the front side has a shape that defines aplurality of horns 114 respectively communicating with the plurality ofslots 112. In this example, the plurality of slots 112 are open to theexternal space respectively through the plurality of horns 114. Byproviding such horns 114, the characteristic impedance within each slotcan be brought gradually closer to the characteristic impedance in freespace, whereby an improved radiation efficiency can be obtained.

FIG. 11A is a perspective view showing one radiating element accordingto still another variant of Embodiment 2. The slot antenna device ofthis example further includes another conductive member 160 having aconductive surface that opposes the conductive surface 110 b on thefront side of the first conductive member 110. The other conductivemember 160 has four other slots 111 in this example. FIG. 11B is adiagram showing the radiating element of FIG. 11A, illustrated so thatthe spacing between the first conductive member 110 and the otherconductive member 160 is exaggerated. In FIGS. 11A and 11B, theplurality of conductive rods 124 extending on both sides of thewaveguide member 122 and the second conductive member 120 having aconductive surface opposing the waveguide face of the waveguide member122 are omitted from illustration.

In FIG. 10, the slots 112 are respectively shown to communicate with thehorns 114; in the example of FIG. 11A, however, the slot 112communicates with a cavity 180. The cavity 180 is a flat hollow spacethat is surrounded by the first conductive surface 110 b, a plurality ofconductive rods 170 on the front side of the first conductive member110, and the conductive surface on the rear side of the conductivemember 160. In this example, the slot 112 is open to the external spacevia the cavity 180. In the examples of FIGS. 11A and 11B, a gap existsbetween the leading ends of the plurality of conductive rods 170 and theconductive surface on the rear side of the other conductive member 160.The roots of the plurality of conductive rods 170 connect to the firstconductive surface 110 b of the first conductive member 110. Aconstruction may be adopted in which the plurality of conductive rods170 are connected to the other conductive member 160. In that case,however, it is ensured that a gap exists between the leading ends of theplurality of conductive rods 170 and the first conductive surface 110 b.

The other conductive member 160 has four other slots 111, such that allslots 111 communicate with the cavity 180. A signal wave which isradiated from the slot 112 into the cavity 180 is radiated toward thefront side of the other conductive member 160 via the four other slots111. Note that a structure may be adopted in which horns are disposed onthe front side of the other conductive member 160, the other slots 111opening at the bottoms of the horns. In this case, a signal wave whichis radiated from the slot 112 is radiated via the cavity 160, the otherslots 111, and the horns.

Horns as shown in FIG. 10 may be provided for the slot antenna device300 having H-shaped slots 112 of Embodiment 1. For example, aconstruction as shown in FIGS. 12A and 12B may be adopted. FIG. 12A is adiagram showing a first conductive member 110 of a slot antenna device300 in which a plurality of horns 114 are provided respectively around aplurality of H-shaped slots 112, as viewed from the rear side. In FIG.12A, the horns 114 that actually are at the back of the plane of thefigure are also illustrated in order to facilitate understanding oftheir relative positioning. FIG. 12B is a cross-sectional view takenalong line B-B in FIG. 12A. In this example, too, providing the horns114 allows to suppress reflection when passing through the slots 112.

Embodiment 3

Next, a third embodiment of the present disclosure will be described. Anantenna device 300 according to the present embodiment includes at leastthree stacked conductive members. The transmitter or receiver isdisposed in a layer that is located more toward the rear side than isthe second conductive member 120.

FIG. 13A is a cross-sectional view schematically showing theconstruction of the antenna device 300 of the present embodiment. Inaddition to a first conductive member 110 and a second conductive member120, the antenna device 300 includes a third conductive member 140.Furthermore, in addition to a first waveguide member 122U that isconnected to the first conductive member 110, the antenna device 300includes a second waveguide member 122L. The second waveguide member122L is disposed between the second conductive member 120 and the thirdconductive member 140.

The first conductive member 110 is basically similar in structure to thefirst conductive member 110 in Embodiment 1 or Embodiment 2. However, inthe present embodiment, two choke structures 150U are provided close toboth ends of the waveguide member 122U. The choke structures 150Urestrain signal waves that are supplied in branches from the centralportion of the row of four slots 112 from propagating beyond the twoslots 112 at opposite ends.

In addition to the third conductive surface 120 a on the front side, thesecond conductive member 120 has a fourth conductive surface 120 b onthe rear side. The second conductive member 120 has a port 145(throughhole) which extends from the third conductive surface 120 athrough to the fourth conductive surface 120 b. The port 145 is opposedto the central portion of the waveguide face 122Ua of the waveguidemember 122U. In other words, as viewed from a direction perpendicular tothe first conductive surface 110 b, the port 145 is located in thecenter of the row of four slots 112.

The third conductive member 140 has a fifth conductive surface 140 a onthe front side, the fifth conductive surface 140 a opposing the fourthconductive surface 120 b. On the fifth conductive surface 140 a of thethird conductive member 140, the ridge-shaped second waveguide member122L is provided.

The second waveguide member 122L extends in the Y direction, along thefourth conductive surface 120 b. The second waveguide member 122L has anelectrically-conductive waveguide face 122La opposing the fourthconductive surface 120 b. The waveguide face 122La also opposes the port145. As viewed from a direction perpendicular to the waveguide face122La, the second waveguide member 122L extends to a position slightlybeyond the port 145.

An artificial magnetic conductor not shown extends on both sides of thesecond waveguide member 122L. The artificial magnetic conductor can berealized by a plurality of conductive rods that are disposed on at leastone of the fourth conductive surface 120 b and the fifth conductivesurface 140 a. The fourth conductive surface 120 b, the waveguide face122La, and the artificial magnetic conductor define a second waveguidein a gap extending between the fourth conductive surface 120 b and thewaveguide face 122La. Via the port 145, the second waveguide isconnected to a first waveguide extending between the waveguide face122Ua of the first waveguide member 122U and the third conductivesurface 120 a of the second conductive member 120. The second waveguideis connected to a transmitter or receiver, either directly or viaanother waveguide not shown.

A choke structure 150L is disposed at an end of the second waveguidemember 122L. In a view resulting by projecting the opening of the port145 onto the waveguide face 122La, a portion spanning the range from theedge to one end of the waveguide member 122L will now be referred to asthe waveguide member end. The choke structure 150L includes one or moreconductive rods 124L that are disposed on the fifth conductive surface140 a, with a gap existing between the waveguide member end and the oneend of the waveguide member 122L. The length of the waveguide member endalong the Y direction is about the same as the length of the choke ridge122Ch along the Y direction. With such a choke structure 150L, leakageof a signal wave propagating along the second waveguide member 122L issuppressed.

In the present embodiment, a signal wave which is supplied from thetransmitter during transmission propagates along the waveguide face122La of the second waveguide member 122L, and passes through the port145 to branch out in two directions. The signal waves having branchedpropagate along the waveguide face 122Ua of the first waveguide member122U, and excite the four slots 112. As viewed from a directionperpendicular to the waveguide face 122Ua, the four slots 112 are insymmetric positions with respect to the port 145. The distances betweenthe centers of these slots 112 are designed so as to be approximatelyequal to the wavelength of a signal wave in the waveguide. Therefore,the four slots 112 are excited with an equal phase. For other purposes,e.g., reducing side lobes, etc., the plurality of slots 112 may beexcited with different phases.

Next, variants of the present embodiment will be described.

FIG. 13B is a cross-sectional view showing a first variant of thepresent embodiment. In this variant, the second waveguide member 122Land the plurality of conductive rods 124L are disposed on the fourthconductive surface 120 b of the second conductive member 120, ratherthan on the fifth conductive surface 140 a of the third conductivemember 140. Therefore, the choke structure 150L is also provided on thefourth conductive surface 120 b. The waveguide face 122La of the secondwaveguide member 122L is opposed to the fifth conductive surface 140 a.The second waveguide member 122L extends alongside the fifth conductivesurface 140 a.

An end face of the second waveguide member 122L is connected to theinner wall surface of the port 145. Although the end face of the secondwaveguide member 122L and the inner wall surface of the port 145 are notshown to be stepped, they may alternatively be stepped. Similarly to thechoke structures 150U on the first conductive member 110, the chokestructure 150L includes a choke ridge 122Lch and one or more conductiverods 124L.

In this variant, the fifth conductive surface 140 a, the waveguide face122La, and the artificial magnetic conductor extending on both sides ofthe waveguide member 122L define a second waveguide in a gap extendingbetween the fifth conductive surface 140 a and the waveguide face 122La.Via the port 145, the second waveguide is connected to a first waveguideextending between the waveguide face 122Ua of the waveguide member 122Uand the third conductive surface 120 a. The second waveguide isconnected to a transmitter or receiver, either directly or via anotherwaveguide not shown.

In the examples shown in FIG. 13A and FIG. 13B, the first waveguidemembers 110 include four slots 112 that are arranged along the Ydirection in which the waveguide member 122U extends. Without beinglimited to four slots 112, there may be five, or even more slots 112.The slots 112 do not need to be in symmetric positions with respect tothe port 145. For example, three ports may be provided in the +Ydirection, and two ports may be provided in the −Y direction, of theport 145. In the case where the first waveguide member 110 has an evennumber of slots 112, the port 145 in the second conductive member 120may be located in the center of the row consisting of the even number ofslots 112, as viewed from a direction perpendicular to the waveguideface 122Ua. With such a construction, two slots 112 that are at equaldistances from the port 145 can be excited with an equal phase.

FIG. 13C is a cross-sectional view showing another variant of thepresent embodiment. In this example, the port 145 in the secondconductive member 120 is located close to one end of the waveguidemember 122U. Therefore, a signal wave propagates from one end to theother end of the waveguide member 122U. In this manner, feeding may beperformed from an end of the waveguide member 122U. Apart from theexample of FIG. 13C, the second waveguide member 122L and the artificialmagnetic conductor extending on both sides thereof may be located on thesecond conductive member 120, in a manner shown in FIG. 13B. Such aconstruction will also provide similar characteristics.

Although each conductive member includes a single waveguide member inthe above embodiment, it may include a plurality of waveguide members.

FIG. 14 is a perspective view showing an exemplary antenna device 300including a plurality of waveguide members 122. The antenna device 300includes a plurality of ridge-shaped waveguide members 122 on the secondconductive surface 110 a of the first conductive member 110. The firstconductive member 110 has a plurality of slots 112. The plurality ofwaveguide members 122 each include a plurality of ridges extending alonga common path. As viewed from a direction perpendicular to the waveguidefaces of the plurality of waveguide members 122, each of the pluralityof slots 112 is located between two adjacent ones of the plurality ofridges. Although FIG. 14 illustrates an example where the slots 112 arein a one-dimensional array, they may constitute a two-dimensional array.To the plurality of slots 112, an identical signal wave that hasbranched out in a feeding path not shown may be supplied, or differentsignal waves may be supplied.

Other Variants

Next, with reference to FIG. 15, exemplary cross-sectional shapes of theport 145 or the slots 111, 112 will be described more specifically. Inthe following description, the port 145 and the slots 111, 112 may becollectively referred to as “throughholes”. Any port 145 or slot 112according to an embodiment of the present disclosure permits thefollowing modifications.

In FIG. 15, (a) shows an exemplary throughhole 1400 a having the shapeof an ellipse. The semimajor axis La of the throughhole 1400 a,indicated by arrowheads in the figure, is chosen so that higher-orderresonance will not occur and that the impedance will not be too small.More specifically, La may be set so that λo/4<La<λo/2, where λo is awavelength in free space corresponding to the center frequency in theoperating frequency band.

In FIG. 15, (b) shows an exemplary throughhole 1400 b having an H shapewhich includes a pair of vertical portions 113L and a lateral portion113T interconnecting the pair of vertical portions 113L. The lateralportion 113T is substantially perpendicular to the pair of verticalportions 113L, and connects between substantial central portions of thepair of vertical portions 113L. The shape and size of such an H-shapedthroughhole 1400 b are also to be determined so that higher-orderresonance will not occur and that the impedance will not be too small.The distance between a point of intersection between the center line g2of the lateral portion 113T and the center line h2 of the entire H shapeperpendicular to the lateral portion 113T and a point of intersectionbetween the center line g2 and the center line k2 of a vertical portion113L is denoted as Lb. The distance between a point of intersectionbetween the center line g2 and the center line k2 and the end of thevertical portion 113L is denoted as Wb. The sum of Lb and Wb is chosenso as to satisfy λo/4<Lb+Wb<λo/2. Choosing the distance Wb to berelatively long allows the distance Lb to be relatively short. As aresult, the width of the H shape along the X direction can be e.g. lessthan λo/2, whereby the interval between the lateral portions 113T alongthe length direction can be made short.

In FIG. 15, (c) shows an exemplary throughhole 1400 c which includes alateral portion 113T and a pair of vertical portions 113L extending fromboth ends of the lateral portion 113T. The directions in which the pairof vertical portions 113L extend from the lateral portion 113T aresubstantially perpendicular to the lateral portion 113T, and areopposite to each other. The distance between a point of intersectionbetween the center line g3 of the lateral portion 113T and the centerline h3 of the overall shape which is perpendicular to the lateralportion 113T and a point of intersection between the center line g3 andthe center line k3 of a vertical portion 113L is denoted as Lc. Thedistance between a point of intersection between the center line g3 andthe center line k3 and the end of the vertical portion 113L is denotedas Wc. The sum of Lc and Wc is chosen so as to satisfy λo/4<Lc+Wc<λo/2.Choosing the distance Wc to be relatively long allows the distance Lc tobe relatively short. As a result, the width along the X direction of theoverall shape in (c) of FIG. 15 can be e.g. less than λo/2, whereby theinterval between the lateral portions 113T along the length directioncan be made short.

In FIG. 15, (d) shows an exemplary throughhole 1400 d which includes alateral portion 113T and a pair of vertical portions 113L extending fromboth ends of the lateral portion 113T in an identical direction which isperpendicular to the lateral portion 113T. Such a shape may be referredto as a “U shape” in the present specification. Note that the shapeshown in (d) of FIG. 15 may be regarded as an upper half shape of an Hshape. The distance between a point of intersection between the centerline g4 of the lateral portion 113T and the center line h4 of theoverall U shape which is perpendicular to the lateral portion 113T and apoint of intersection between the center line g4 and the center line k4of a vertical portion 113L is denoted as Ld. The distance between apoint of intersection between the center line g4 and the center line k4and the end of the vertical portion 113L is denoted as Wd. The sum of Ldand Wd is chosen so as to satisfy λo/4<Ld+Wd<λo/2. Choosing the distanceWd to be relatively long allows the distance Ld to be relatively short.As a result, the width along the X direction of the U shape can be e.g.less than λo/2, whereby the interval between the lateral portions 113Talong the length direction can be made short.

Next, variants of waveguide structures including the waveguide member122, the conductive members 110 and 120, and the conductive rods 124will be described. The following variants are applicable to the WRGstructure in any place in each embodiment described above.

FIG. 16A is a cross-sectional view showing an exemplary structure inwhich only the waveguide face 122 a, defining an upper face of thewaveguide member 122, is electrically conductive, while any portion ofthe waveguide member 122 other than the waveguide face 122 a is notelectrically conductive. Both of the conductive member 110 and theconductive member 120 alike are only electrically conductive at theirsurface that has the waveguide member 122 provided thereon (i.e., theconductive surface 110 a, 120 a), while not being electricallyconductive in any other portions. Thus, each of the waveguide member122, the conductive member 110, and the conductive member 120 does notneed to be electrically conductive.

FIG. 16B is a diagram showing a variant in which the waveguide member122 is not formed on the conductive member 120. In this example, thewaveguide member 122 is fixed to a supporting member (e.g., the innerwall of the housing) that supports the conductive member 110 and theconductive member. A gap exists between the waveguide member 122 and theconductive member 120. Thus, the waveguide member 122 does not need tobe connected to the conductive member 120.

FIG. 16C is a diagram showing an exemplary structure where theconductive member 120, the waveguide member 122, and each of theplurality of conductive rods 124 are composed of a dielectric surfacethat is coated with an electrically conductive material such as a metal.The conductive member 120, the waveguide member 122, and the pluralityof conductive rods 124 are connected to one another via the electricalconductor. On the other hand, the conductive member 110 is made of anelectrically conductive material such as a metal.

FIG. 16D and FIG. 16E are diagrams each showing an exemplary structurein which dielectric layers 110 c and 120 c are respectively provided onthe outermost surfaces of conductive members 110 and 120, a waveguidemember 122, and conductive rods 124. FIG. 16D shows an exemplarystructure in which the surface of metal conductive members, which areelectrical conductors, are covered with a dielectric layer. FIG. 16Eshows an example where the conductive member 120 is structured so thatthe surface of members which are composed of a dielectric, e.g., resin,is covered with an electrical conductor such as a metal, this metallayer being further coated with a dielectric layer. The dielectric layerthat covers the metal surface may be a coating of resin or the like, oran oxide film of passivation coating or the like which is generated asthe metal becomes oxidized.

The dielectric layer on the outermost surface will allow losses to beincreased in the electromagnetic wave propagating through the WRGwaveguide, but is able to protect the conductive surfaces 110 a and 120a (which are electrically conductive) from corrosion. It also preventsinfluences of a DC voltage, or an AC voltage of such a low frequencythat it is not capable of propagation on certain WRG waveguides.

FIG. 16F is a diagram showing an example where the height of thewaveguide member 122 is lower than the height of the conductive rods124, and the portion of the conductive surface 110 a of the conductivemember 110 that opposes the waveguide face 122 a protrudes toward thewaveguide member 122. Even such a structure will operate in a similarmanner to the above-described embodiment, so long as the ranges ofdimensions depicted in FIG. 4 are satisfied.

FIG. 16G is a diagram showing an example where, further in the structureof FIG. 16F, portions of the conductive surface 110 a that oppose theconductive rods 124 protrude toward the conductive rods 124. Even such astructure will operate in a similar manner to the above-describedembodiment, so long as the ranges of dimensions depicted in FIG. 4 aresatisfied. Instead of a structure in which the conductive surface 110 apartially protrudes, a structure in which the conductive surface 110 ais partially dented may be adopted.

FIG. 17A is a diagram showing an example where a conductive surface 110a of the conductive member 110 is shaped as a curved surface. FIG. 17Bis a diagram showing an example where also a conductive surface 120 a ofthe conductive member 120 is shaped as a curved surface. As demonstratedby these examples, the conductive surfaces 110 a and 120 a may not beshaped as planes, but may be shaped as curved surfaces. A conductivemember having a conductive surface which is a curved surface is alsoqualifies as a conductive member having a “plate shape”.

In the waveguide device 100 of the above-described construction, asignal wave of the operating frequency is unable to propagate in thespace between the surface 125 of the artificial magnetic conductor andthe conductive surface 110 a of the conductive member 110, butpropagates in the space between the waveguide face 122 a of thewaveguide member 122 and the conductive surface 110 a of the conductivemember 110. Unlike in a hollow waveguide, the width of the waveguidemember 122 in such a waveguide structure does not need to be equal to orgreater than a half of the wavelength of the electromagnetic wave topropagate. Moreover, the conductive member 110 and the conductive member120 do not need to be electrically interconnected by a metal wall thatextends along the thickness direction (i.e., in parallel to the YZplane).

A slot antenna device according to an embodiment of the presentdisclosure can be suitably used in a radar device or a radar system tobe incorporated in moving entities such as vehicles, marine vessels,aircraft, robots, or the like, for example. A radar device would includea slot antenna device according to an embodiment of the presentdisclosure and a microwave integrated circuit that is connected to theslot antenna device. A radar system would include the radar device and asignal processing circuit that is connected to the microwave integratedcircuit of the radar device. An antenna device according to anembodiment of the present disclosure includes a multilayered WRGstructure which permits downsizing, and thus allows the area of the faceon which antenna elements are arrayed to be significantly reduced, ascompared to a construction in which a conventional hollow waveguide isused. Therefore, a radar system incorporating the antenna device can beeasily mounted in a narrow place such as a face of a rearview mirror ina vehicle that is opposite to its specular surface, or a small-sizedmoving entity such as a UAV (an Unmanned Aerial Vehicle, a so-calleddrone). Note that, without being limited to the implementation where itis mounted in a vehicle, a radar system may be used while being fixed onthe road or a building, for example.

A slot antenna device according to an embodiment of the presentdisclosure can also be used in a wireless communication system. Such awireless communication system would include a slot antenna deviceaccording to any of the above embodiments and a communication circuit (atransmission circuit or a reception circuit). Details of exemplaryapplications to wireless communication systems will be described later.

A slot antenna device according to an embodiment of the presentdisclosure can further be used as an antenna in an indoor positioningsystem (IPS). An indoor positioning system is able to identify theposition of a moving entity, such as a person or an automated guidedvehicle (AGV), that is in a building. An antenna device can also be usedas a radio wave transmitter (beacon) for use in a system which providesinformation to an information terminal device (e.g., a smartphone) thatis carried by a person who has visited a store or any other facility. Insuch a system, once every several seconds, a beacon may radiate anelectromagnetic wave carrying an ID or other information superposedthereon, for example. When the information terminal device receives thiselectromagnetic wave, the information terminal device transmits thereceived information to a remote server computer via telecommunicationlines. Based on the information that has been received from theinformation terminal device, the server computer identifies the positionof that information terminal device, and provides information which isassociated with that position (e.g., product information or a coupon) tothe information terminal device.

The present specification employs the term “artificial magneticconductor” in describing the technique according to the presentdisclosure, this being in line with what is set forth in a paper by oneof the inventors Kirino (Non-Patent Document 1) as well as a paper byKildal et al., who published a study directed to related subject matteraround the same time. However, it has been found through a study by theinventors that the invention according to the present disclosure doesnot necessarily require an “artificial magnetic conductor” under itsconventional definition. That is, while a periodic structure has beenbelieved to be a requirement for an artificial magnetic conductor, theinvention according to the present disclosure does not necessary requirea periodic structure in order to be practiced.

The artificial magnetic conductor that is described in the presentdisclosure consists of rows of conductive rods. Therefore, in order tostop the electromagnetic waves leaking away from the waveguide face, ithas been believed essential that there exist at least two rows ofconductive rods on one side of the waveguide member(s), such rows ofconductive rods extending along the waveguide member(s) (ridge(s)). Thereason is that it takes at least two rows of conductive rods for them tohave a “period”. However, according to a study by the inventors, evenwhen only one row of conductive rods exists between two waveguidemembers that extend in parallel to each other, the intensity of a signalthat leaks from one waveguide member to the other waveguide member canbe suppressed to −10 dB or less, which is a practically sufficient valuein many applications. The reason why such a sufficient level ofseparation is achieved with only an imperfect periodic structure is sofar unclear. However, in view of this fact, in the present disclosure,the notion of “artificial magnetic conductor” is extended so that theterm also encompasses a structure including only one row of conductiverods for convenience sake.

APPLICATION EXAMPLE 1 Onboard Radar System

Next, as an Application Example of utilizing the above-described slotarray antenna, an instance of an onboard radar system including a slotarray antenna will be described. A transmission wave used in an onboardradar system may have a frequency of e.g. 76 gigahertz (GHz) band, whichwill have a wavelength λo of about 4 mm in free space.

In safety technology of automobiles, e.g., collision avoidance systemsor automated driving, it is particularly essential to identify one ormore vehicles (targets) that are traveling ahead of the driver'svehicle. As a method of identifying vehicles, techniques of estimatingthe directions of arriving waves by using a radar system have been underdevelopment.

FIG. 18 shows a driver's vehicle 500, and a preceding vehicle 502 thatis traveling in the same lane as the driver's vehicle 500. The driver'svehicle 500 includes an onboard radar system which incorporates a slotarray antenna according to any of the above-described embodiments. Whenthe onboard radar system of the driver's vehicle 500 radiates a radiofrequency transmission signal, the transmission signal reaches thepreceding vehicle 502 and is reflected therefrom, so that a part of thesignal returns to the driver's vehicle 500. The onboard radar systemreceives this signal to calculate a position of the preceding vehicle502, a distance (“range”) to the preceding vehicle 502, velocity, etc.

FIG. 19 shows the onboard radar system 510 of the driver's vehicle 500.The onboard radar system 510 is provided within the vehicle. Morespecifically, the onboard radar system 510 is disposed on a face of therearview mirror that is opposite to its specular surface. From withinthe vehicle, the onboard radar system 510 radiates a radio frequencytransmission signal in the direction of travel of the vehicle 500, andreceives a signal(s) which arrives from the direction of travel.

The onboard radar system 510 of this Application Example includes a slotarray antenna according to an embodiment of the present disclosure. Theslot array antenna may include a plurality of waveguide members that areparallel to one another. They are to be arranged so that the pluralityof waveguide members each extend in a direction which coincides with thevertical direction, and that the plurality of waveguide members arearranged in a direction which coincides with the horizontal direction.As a result, the lateral and vertical dimensions of the plurality ofslots as viewed from the front can be further reduced.

Exemplary dimensions of an antenna device including the above arrayantenna may be 60 mm (wide)×30 mm (long)×10 mm (deep). It will beappreciated that this is a very small size for a millimeter wave radarsystem of the 76 GHz band.

Note that many a conventional onboard radar system is provided outsidethe vehicle, e.g., at the tip of the front nose. The reason is that theonboard radar system is relatively large in size, and thus is difficultto be provided within the vehicle as in the present disclosure. Theonboard radar system 510 of this Application Example may be installedwithin the vehicle as described above, but may instead be mounted at thetip of the front nose. Since the footprint of the onboard radar systemon the front nose is reduced, other parts can be more easily placed.

The Application Example allows the interval between a plurality ofwaveguide members (ridges) that are used in the transmission antenna tobe narrow, which also narrows the interval between a plurality of slotsto be provided opposite from a number of adjacent waveguide members.This reduces the influences of grating lobes. For example, when theinterval between the centers of two laterally adjacent slots is shorterthan the free-space wavelength λo of the transmission wave (i.e., lessthan about 4 mm), no grating lobes will occur frontward. As a result,influences of grating lobes are reduced. Note that grating lobes willoccur when the interval at which the antenna elements are arrayed isgreater than a half of the wavelength of an electromagnetic wave. If theinterval at which the antenna elements are arrayed is less than thewavelength, no grating lobes will occur frontward. Therefore, in thecase where no beam steering is performed to impart phase differencesamong the radio waves radiated from the respective antenna elementscomposing an array antenna, grating lobes will exert substantially noinfluences so long as the interval at which the antenna elements arearrayed is smaller than the wavelength. By adjusting the array factor ofthe transmission antenna, the directivity of the transmission antennacan be adjusted. A phase shifter may be provided so as to be able toindividually adjust the phases of electromagnetic waves that aretransmitted on plural waveguide members. In that case, even if theinterval between antenna elements is made less than the free-spacewavelength λo of the transmission wave, grating lobes will appear as thephase shift amount is increased. However, when the intervals between theantenna elements is reduced to less than a half of the free spacewavelength λo of the transmission wave, grating lobes will not appearirrespective of the phase shift amount. By providing a phase shifter,the directivity of the transmission antenna can be changed in anydesired direction. Since the construction of a phase shifter iswell-known, description thereof will be omitted.

A reception antenna according to the Application Example is able toreduce reception of reflected waves associated with grating lobes,thereby being able to improve the precision of the below-describedprocessing. Hereinafter, an example of a reception process will bedescribed.

FIG. 20A shows a relationship between an array antenna AA of the onboardradar system 510 and plural arriving waves k (k: an integer from 1 to K;the same will always apply below. K is the number of targets that arepresent in different azimuths). The array antenna AA includes M antennaelements in a linear array. Principlewise, an antenna can be used forboth transmission and reception, and therefore the array antenna AA canbe used for both a transmission antenna and a reception antenna.Hereinafter, an example method of processing an arriving wave which isreceived by the reception antenna will be described.

The array antenna AA receives plural arriving waves that simultaneouslyimpinge at various angles. Some of the plural arriving waves may bearriving waves which have been radiated from the transmission antenna ofthe same onboard radar system 510 and reflected by a target(s).Furthermore, some of the plural arriving waves may be direct or indirectarriving waves that have been radiated from other vehicles.

The incident angle of each arriving wave (i.e., an angle representingits direction of arrival) is an angle with respect to the broadside B ofthe array antenna AA. The incident angle of an arriving wave representsan angle with respect to a direction which is perpendicular to thedirection of the line along which antenna elements are arrayed.

Now, consider a k^(th) arriving wave. Where K arriving waves areimpinging on the array antenna from K targets existing at differentazimuths, a “k^(th) arriving wave” means an arriving wave which isidentified by an incident angle θ_(k).

FIG. 20B shows the array antenna AA receiving the k^(th) arriving wave.The signals received by the array antenna AA can be expressed as a“vector” having M elements, by Math. 1.

S=[s₁, s₂, . . . , s_(M]) ^(T)   (Math. 1)

In the above, s_(m) (where m is an integer from 1 to M; the same willalso be true hereinbelow) is the value of a signal which is received byan m^(th) antenna element. The superscript ^(T) means transposition. Sis a column vector. The column vector S is defined by a product ofmultiplication between a direction vector (referred to as a steeringvector or a mode vector) as determined by the construction of the arrayantenna and a complex vector representing a signal from each target(also referred to as a wave source or a signal source). When the numberof wave sources is K, the waves of signals arriving at each individualantenna element from the respective K wave sources are linearlysuperposed. In this state, s_(m) can be expressed by Math. 2.

$\begin{matrix}{s_{m} = {\sum\limits_{k = 1}^{K}{a_{k}\exp \left\{ {j\left( {{\frac{2\pi}{\lambda}d_{m}\sin \; \theta_{k}} + \phi_{k}} \right)} \right\}}}} & \left\lbrack {{Math}.\mspace{11mu} 2} \right\rbrack\end{matrix}$

In Math. 2, a_(k), θ_(k) and ϕ_(k) respectively denote the amplitude,incident angle, and initial phase of the k^(th) arriving wave. Moreover,λ denotes the wavelength of an arriving wave, and j is an imaginaryunit.

As will be understood from Math. 2, s_(m) is expressed as a complexnumber consisting of a real part (Re) and an imaginary part (Im).

When this is further generalized by taking noise (internal noise orthermal noise) into consideration, the array reception signal X can beexpressed as Math. 3.

X=S+N   (Math. 3)

N is a vector expression of noise.

The signal processing circuit generates a spatial covariance matrix Rxx(Math. 4) of arriving waves by using the array reception signal Xexpressed by Math. 3, and further determines eigenvalues of the spatialcovariance matrix Rxx.

$\begin{matrix}\begin{matrix}{R_{xx} = {XX}^{H}} \\{= \begin{bmatrix}{Rxx}_{11} & \ldots & {Rxx}_{1M} \\\vdots & \ddots & \vdots \\{Rxx}_{M\; 1} & \ldots & {Rxx}_{MM}\end{bmatrix}}\end{matrix} & \left\lbrack {{Math}.\mspace{11mu} 4} \right\rbrack\end{matrix}$

In the above, the superscript ^(H) means complex conjugate transposition(Hermitian conjugate).

Among the eigenvalues, the number of eigenvalues which have values equalto or greater than a predetermined value that is defined based onthermal noise (signal space eigenvalues) corresponds to the number ofarriving waves. Then, angles that produce the highest likelihood as tothe directions of arrival of reflected waves (i.e. maximum likelihood)are calculated, whereby the number of targets and the angles at whichthe respective targets are present can be identified. This process isknown as a maximum likelihood estimation technique.

Next, see FIG. 21. FIG. 21 is a block diagram showing an exemplaryfundamental construction of a vehicle travel controlling apparatus 600according to the present disclosure. The vehicle travel controllingapparatus 600 shown in FIG. 21 includes a radar system 510 which ismounted in a vehicle, and a travel assistance electronic controlapparatus 520 which is connected to the radar system 510. The radarsystem 510 includes an array antenna AA and a radar signal processingapparatus 530.

The array antenna AA includes a plurality of antenna elements, each ofwhich outputs a reception signal in response to one or plural arrivingwaves. As mentioned earlier, the array antenna AA is capable ofradiating a millimeter wave of a high frequency.

In the radar system 510, the array antenna AA needs to be attached tothe vehicle, while at least some of the functions of the radar signalprocessing apparatus 530 may be implemented by a computer 550 and adatabase 552 which are provided externally to the vehicle travelcontrolling apparatus 600 (e.g., outside of the driver's vehicle). Inthat case, the portions of the radar signal processing apparatus 530that are located within the vehicle may be perpetually or occasionallyconnected to the computer 550 and database 552 external to the vehicleso that bidirectional communications of signal or data are possible. Thecommunications are to be performed via a communication device 540 of thevehicle and a commonly-available communications network.

The database 552 may store a program which defines various signalprocessing algorithms. The content of the data and program needed forthe operation of the radar system 510 may be externally updated via thecommunication device 540. Thus, at least some of the functions of theradar system 510 can be realized externally to the driver's vehicle(which is inclusive of the interior of another vehicle), by a cloudcomputing technique. Therefore, an “onboard” radar system in the meaningof the present disclosure does not require that all of its constituentelements be mounted within the (driver's) vehicle. However, forsimplicity, the present application will describe an implementation inwhich all constituent elements according to the present disclosure aremounted in a single vehicle (i.e., the driver's vehicle), unlessotherwise specified.

The radar signal processing apparatus 530 includes a signal processingcircuit 560. The signal processing circuit 560 directly or indirectlyreceives reception signals from the array antenna AA, and inputs thereception signals, or a secondary signal(s) which has been generatedfrom the reception signals, to an arriving wave estimation unit AU. Apart or a whole of the circuit (not shown) which generates a secondarysignal(s) from the reception signals does not need to be provided insideof the signal processing circuit 560. A part or a whole of such acircuit (preprocessing circuit) may be provided between the arrayantenna AA and the radar signal processing apparatus 530.

The signal processing circuit 560 is configured to perform computationby using the reception signals or secondary signal(s), and output asignal indicating the number of arriving waves. As used herein, a“signal indicating the number of arriving waves” can be said to be asignal indicating the number of preceding vehicles (which may be onepreceding vehicle or plural preceding vehicles) ahead of the driver'svehicle.

The signal processing circuit 560 may be configured to execute varioussignal processing which is executable by known radar signal processingapparatuses. For example, the signal processing circuit 560 may beconfigured to execute “super-resolution algorithms” such as the MUSICmethod, the ESPRIT method, or the SAGE method, or other algorithms fordirection-of-arrival estimation of relatively low resolution.

The arriving wave estimation unit AU shown in FIG. 21 estimates an anglerepresenting the azimuth of each arriving wave by an arbitrary algorithmfor direction-of-arrival estimation, and outputs a signal indicating theestimation result. The signal processing circuit 560 estimates thedistance to each target as a wave source of an arriving wave, therelative velocity of the target, and the azimuth of the target by usinga known algorithm which is executed by the arriving wave estimation unitAU, and output a signal indicating the estimation result.

In the present disclosure, the term “signal processing circuit” is notlimited to a single circuit, but encompasses any implementation in whicha combination of plural circuits is conceptually regarded as a singlefunctional part. The signal processing circuit 560 may be realized byone or more System-on-Chips (SoCs). For example, a part or a whole ofthe signal processing circuit 560 may be an FPGA (Field-ProgrammableGate Array), which is a programmable logic device (PLD). In that case,the signal processing circuit 560 includes a plurality of computationelements (e.g., general-purpose logics and multipliers) and a pluralityof memory elements (e.g., look-up tables or memory blocks).Alternatively, the signal processing circuit 560 may be a set of ageneral-purpose processor(s) and a main memory device(s). The signalprocessing circuit 560 may be a circuit which includes a processorcore(s) and a memory device(s). These may function as the signalprocessing circuit 560.

The travel assistance electronic control apparatus 520 is configured toprovide travel assistance for the vehicle based on various signals whichare output from the radar signal processing apparatus 530. The travelassistance electronic control apparatus 520 instructs various electroniccontrol units to fulfill predetermined functions, e.g., a function ofissuing an alarm to prompt the driver to make a braking operation whenthe distance to a preceding vehicle (vehicular gap) has become shorterthan a predefined value; a function of controlling the brakes; and afunction of controlling the accelerator. For example, in the case of anoperation mode which performs adaptive cruise control of the driver'svehicle, the travel assistance electronic control apparatus 520 sendspredetermined signals to various electronic control units (not shown)and actuators, to maintain the distance of the driver's vehicle to apreceding vehicle at a predefined value, or maintain the travelingvelocity of the driver's vehicle at a predefined value.

In the case of the MUSIC method, the signal processing circuit 560determines eigenvalues of the spatial covariance matrix, and, as asignal indicating the number of arriving waves, outputs a signalindicating the number of those eigenvalues (“signal space eigenvalues”)which are greater than a predetermined value (thermal noise power) thatis defined based on thermal noise.

Next, see FIG. 22. FIG. 22 is a block diagram showing another exemplaryconstruction for the vehicle travel controlling apparatus 600. The radarsystem 510 in the vehicle travel controlling apparatus 600 of FIG. 22includes an array antenna AA, which includes an array antenna that isdedicated to reception only (also referred to as a reception antenna) Rxand an array antenna that is dedicated to transmission only (alsoreferred to as a transmission antenna) Tx; and an object detectionapparatus 570.

At least one of the transmission antenna Tx and the reception antenna Rxhas the aforementioned waveguide structure. The transmission antenna Txradiates a transmission wave, which may be a millimeter wave, forexample. The reception antenna Rx that is dedicated to reception onlyoutputs a reception signal in response to one or plural arriving waves(e.g., a millimeter wave(s)).

A transmission/reception circuit 580 sends a transmission signal for atransmission wave to the transmission antenna Tx, and performs“preprocessing” for reception signals of reception waves received at thereception antenna Rx. A part or a whole of the preprocessing may beperformed by the signal processing circuit 560 in the radar signalprocessing apparatus 530. A typical example of preprocessing to beperformed by the transmission/reception circuit 580 may be generating abeat signal from a reception signal, and converting a reception signalof analog format into a reception signal of digital format.

In the present specification, any device that includes a transmissionantenna, a reception antenna, a transmission/reception circuit, and awaveguide device which allows electromagnetic waves to propagate betweenthe transmission antenna and reception antenna and thetransmission/reception circuit is referred to as a “radar device”.Moreover, a system that includes a signal processing apparatus(including a signal processing circuit), e.g., an object detectionapparatus, in addition to a radar device is referred to as a “radarsystem”.

Note that the radar system according to the present disclosure may,without being limited to the implementation where it is mounted in thedriver's vehicle, be used while being fixed on the road or a building.

Next, an example of a more specific construction of the vehicle travelcontrolling apparatus 600 will be described.

FIG. 23 is a block diagram showing an example of a more specificconstruction of the vehicle travel controlling apparatus 600. Thevehicle travel controlling apparatus 600 shown in FIG. 23 includes aradar system 510 and an onboard camera system 700. The radar system 510includes an array antenna AA, a transmission/reception circuit 580 whichis connected to the array antenna AA, and a signal processing circuit560.

The onboard camera system 700 includes an onboard camera 710 which ismounted in a vehicle, and an image processing circuit 720 whichprocesses an image or video that is acquired by the onboard camera 710.

The vehicle travel controlling apparatus 600 of this Application Exampleincludes an object detection apparatus 570 which is connected to thearray antenna AA and the onboard camera 710, and a travel assistanceelectronic control apparatus 520 which is connected to the objectdetection apparatus 570. The object detection apparatus 570 includes atransmission/reception circuit 580 and an image processing circuit 720,in addition to the above-described radar signal processing apparatus 530(including the signal processing circuit 560). The object detectionapparatus 570 detects a target on the road or near the road, by usingnot only the information which is obtained by the radar system 510 butalso the information which is obtained by the image processing circuit720. For example, while the driver's vehicle is traveling in one of twoor more lanes of the same direction, the image processing circuit 720can distinguish which lane the driver's vehicle is traveling in, andsupply that result of distinction to the signal processing circuit 560.When the number and azimuth(s) of preceding vehicles are to berecognized by using a predetermined algorithm for direction-of-arrivalestimation (e.g., the MUSIC method), the signal processing circuit 560is able to provide more reliable information concerning a spatialdistribution of preceding vehicles by referring to the information fromthe image processing circuit 720.

Note that the onboard camera system 700 is an example of a means foridentifying which lane the driver's vehicle is traveling in. The laneposition of the driver's vehicle may be identified by any other means.For example, by utilizing an ultra-wide band (UWB) technique, it ispossible to identify which one of a plurality of lanes the driver'svehicle is traveling in. It is widely known that the ultra-wide bandtechnique is applicable to position measurement and/or radar. Using theultra-wide band technique enhances the range resolution of the radar, sothat, even when a large number of vehicles exist ahead, each individualtarget can be detected with distinction, based on differences indistance. This makes it possible to accurately identify distance from aguardrail on the road shoulder, or from the median strip. The width ofeach lane is predefined based on each country's law or the like. Byusing such information, it becomes possible to identify where the lanein which the driver's vehicle is currently traveling is. Note that theultra-wide band technique is an example. A radio wave based on any otherwireless technique may be used. Moreover, LIDAR (Light Detection andRanging) may be used together with a radar. LIDAR is sometimes called“laser radar”.

The array antenna AA may be a generic millimeter wave array antenna foronboard use. The transmission antenna Tx in this Application Exampleradiates a millimeter wave as a transmission wave ahead of the vehicle.A portion of the transmission wave is reflected off a target which istypically a preceding vehicle, whereby a reflected wave occurs from thetarget being a wave source. A portion of the reflected wave reaches thearray antenna (reception antenna) AA as an arriving wave. Each of theplurality of antenna elements of the array antenna AA outputs areception signal in response to one or plural arriving waves. In thecase where the number of targets functioning as wave sources ofreflected waves is K (where K is an integer of one or more), the numberof arriving waves is K, but this number K of arriving waves is not knownbeforehand.

The example of FIG. 21 assumes that the radar system 510 is provided asan integral piece, including the array antenna AA, on the rearviewmirror. However, the number and positions of array antennas AA are notlimited to any specific number or specific positions. An array antennaAA may be disposed on the rear surface of the vehicle so as to be ableto detect targets that are behind the vehicle. Moreover, a plurality ofarray antennas AA may be disposed on the front surface and the rearsurface of the vehicle. The array antenna(s) AA may be disposed insidethe vehicle. Even in the case where a horn antenna whose respectiveantenna elements include horns as mentioned above is to be adopted asthe array antenna(s) AA, the array antenna(s) with such antenna elementsmay be situated inside the vehicle.

The signal processing circuit 560 receives and processes the receptionsignals which have been received by the reception antenna Rx andsubjected to preprocessing by the transmission/reception circuit 580.This process encompasses inputting the reception signals to the arrivingwave estimation unit AU, or alternatively, generating a secondarysignal(s) from the reception signals and inputting the secondarysignal(s) to the arriving wave estimation unit AU.

In the example of FIG. 23, a selection circuit 596 which receives thesignal being output from the signal processing circuit 560 and thesignal being output from the image processing circuit 720 is provided inthe object detection apparatus 570. The selection circuit 596 allows oneor both of the signal being output from the signal processing circuit560 and the signal being output from the image processing circuit 720 tobe fed to the travel assistance electronic control apparatus 520.

FIG. 24 is a block diagram showing a more detailed exemplaryconstruction of the radar system 510 according to this ApplicationExample.

As shown in FIG. 24, the array antenna AA includes a transmissionantenna Tx which transmits a millimeter wave and reception antennas Rxwhich receive arriving waves reflected from targets. Although only onetransmission antenna Tx is illustrated in the figure, two or more kindsof transmission antennas with different characteristics may be provided.The array antenna AA includes M antenna elements 11 ₁, 11 ₂, . . . , 11_(M) (where M is an integer of 3 or more). In response to the arrivingwaves, the plurality of antenna elements 11 ₁, 11 ₂, . . . , 11 _(M)respectively output reception signals s₁, s₂, . . . , s_(M) (FIG. 20B).

In the array antenna AA, the antenna elements 11 ₁ to 11 _(M) arearranged in a linear array or a two-dimensional array at fixedintervals, for example. Each arriving wave will impinge on the arrayantenna AA from a direction at an angle θ with respect to the normal ofthe plane in which the antenna elements 11 ₁ to 11 _(M) are arrayed.Thus, the direction of arrival of an arriving wave is defined by thisangle θ.

When an arriving wave from one target impinges on the array antenna AA,this approximates to a plane wave impinging on the antenna elements 11 ₁to 11 _(M) from azimuths of the same angle θ. When K arriving wavesimpinge on the array antenna AA from K targets with different azimuths,the individual arriving waves can be identified in terms of respectivelydifferent angles θ₁ to θ_(K).

As shown in FIG. 24, the object detection apparatus 570 includes thetransmission/reception circuit 580 and the signal processing circuit560.

The transmission/reception circuit 580 includes a triangular wavegeneration circuit 581, a VCO (voltage controlled oscillator) 582, adistributor 583, mixers 584, filters 585, a switch 586, an A/D converter587, and a controller 588. Although the radar system in this ApplicationExample is configured to perform transmission and reception ofmillimeter waves by the FMCW method, the radar system of the presentdisclosure is not limited to this method. The transmission/receptioncircuit 580 is configured to generate a beat signal based on a receptionsignal from the array antenna AA and a transmission signal from thetransmission antenna Tx.

The signal processing circuit 560 includes a distance detection section533, a velocity detection section 534, and an azimuth detection section536. The signal processing circuit 560 is configured to process a signalfrom the A/D converter 587 in the transmission/reception circuit 580,and output signals respectively indicating the detected distance to thetarget, the relative velocity of the target, and the azimuth of thetarget.

First, the construction and operation of the transmission/receptioncircuit 580 will be described in detail.

The triangular wave generation circuit 581 generates a triangular wavesignal, and supplies it to the VCO 582. The VCO 582 outputs atransmission signal having a frequency as modulated based on thetriangular wave signal. FIG. 25 is a diagram showing change in frequencyof a transmission signal which is modulated based on the signal that isgenerated by the triangular wave generation circuit 581. This waveformhas a modulation width Δf and a center frequency of f0. The transmissionsignal having a thus modulated frequency is supplied to the distributor583. The distributor 583 allows the transmission signal obtained fromthe VCO 582 to be distributed among the mixers 584 and the transmissionantenna Tx. Thus, the transmission antenna radiates a millimeter wavehaving a frequency which is modulated in triangular waves, as shown inFIG. 25.

In addition to the transmission signal, FIG. 25 also shows an example ofa reception signal from an arriving wave which is reflected from asingle preceding vehicle. The reception signal is delayed from thetransmission signal. This delay is in proportion to the distance betweenthe driver's vehicle and the preceding vehicle. Moreover, the frequencyof the reception signal increases or decreases in accordance with therelative velocity of the preceding vehicle, due to the Doppler effect.

When the reception signal and the transmission signal are mixed, a beatsignal is generated based on their frequency difference. The frequencyof this beat signal (beat frequency) differs between a period in whichthe transmission signal increases in frequency (ascent) and a period inwhich the transmission signal decreases in frequency (descent). Once abeat frequency for each period is determined, based on such beatfrequencies, the distance to the target and the relative velocity of thetarget are calculated.

FIG. 26 shows a beat frequency fu in an “ascent” period and a beatfrequency fd in a “descent” period. In the graph of FIG. 26, thehorizontal axis represents frequency, and the vertical axis representssignal intensity. This graph is obtained by subjecting the beat signalto time-frequency conversion. Once the beat frequencies fu and fd areobtained, based on a known equation, the distance to the target and therelative velocity of the target are calculated. In this ApplicationExample, with the construction and operation described below, beatfrequencies corresponding to each antenna element of the array antennaAA are obtained, thus enabling estimation of the position information ofa target.

In the example shown in FIG. 24, reception signals from channels Ch₁ toCh_(M) corresponding to the respective antenna elements 11 ₁ to 11 _(M)are each amplified by an amplifier, and input to the correspondingmixers 584. Each mixer 584 mixes the transmission signal into theamplified reception signal. Through this mixing, a beat signal isgenerated corresponding to the frequency difference between thereception signal and the transmission signal. The generated beat signalis fed to the corresponding filter 585. The filters 585 apply bandwidthcontrol to the beat signals on the channels Ch₁ to Ch_(M), and supplybandwidth-controlled beat signals to the switch 586.

The switch 586 performs switching in response to a sampling signal whichis input from the controller 588. The controller 588 may be composed ofa microcomputer, for example. Based on a computer program which isstored in a memory such as a ROM, the controller 588 controls the entiretransmission/reception circuit 580. The controller 588 does not need tobe provided inside the transmission/reception circuit 580, but may beprovided inside the signal processing circuit 560. In other words, thetransmission/reception circuit 580 may operate in accordance with acontrol signal from the signal processing circuit 560. Alternatively,some or all of the functions of the controller 588 may be realized by acentral processing unit which controls the entire transmission/receptioncircuit 580 and signal processing circuit 560.

The beat signals on the channels Ch₁ to Ch_(M) having passed through therespective filters 585 are consecutively supplied to the A/D converter587 via the switch 586. In synchronization with the sampling signal, theA/D converter 587 converts the beat signals on the channels Ch₁ toCh_(M), which are input from the switch 586, into digital signals.

Hereinafter, the construction and operation of the signal processingcircuit 560 will be described in detail. In this Application Example,the distance to the target and the relative velocity of the target areestimated by the FMCW method. Without being limited to the FMCW methodas described below, the radar system can also be implemented by usingother methods, e.g., 2 frequency CW and spread spectrum methods.

In the example shown in FIG. 24, the signal processing circuit 560includes a memory 531, a reception intensity calculation section 532, adistance detection section 533, a velocity detection section 534, a DBF(digital beam forming) processing section 535, an azimuth detectionsection 536, a target link processing section 537, a matrix generationsection 538, a target output processing section 539, and an arrivingwave estimation unit AU. As mentioned earlier, a part or a whole of thesignal processing circuit 560 may be implemented by FPGA, or by a set ofa general-purpose processor(s) and a main memory device(s). The memory531, the reception intensity calculation section 532, the DBF processingsection 535, the distance detection section 533, the velocity detectionsection 534, the azimuth detection section 536, the target linkprocessing section 537, and the arriving wave estimation unit AU may beindividual parts that are implemented in distinct pieces of hardware, orfunctional blocks of a single signal processing circuit.

FIG. 27 shows an exemplary implementation in which the signal processingcircuit 560 is implemented in hardware including a processor PR and amemory device MD. In the signal processing circuit 560 with thisconstruction, too, a computer program that is stored in the memorydevice MD may fulfill the functions of the reception intensitycalculation section 532, the DBF processing section 535, the distancedetection section 533, the velocity detection section 534, the azimuthdetection section 536, the target link processing section 537, thematrix generation section 538, and the arriving wave estimation unit AUshown in FIG. 24.

The signal processing circuit 560 in this Application Example isconfigured to estimate the position information of a preceding vehicleby using each beat signal converted into a digital signal as a secondarysignal of the reception signal, and output a signal indicating theestimation result. Hereinafter, the construction and operation of thesignal processing circuit 560 in this Application Example will bedescribed in detail.

For each of the channels Ch₁ to Ch_(M), the memory 531 in the signalprocessing circuit 560 stores a digital signal which is output from theA/D converter 587. The memory 531 may be composed of a generic storagemedium such as a semiconductor memory or a hard disk and/or an opticaldisk.

The reception intensity calculation section 532 applies Fouriertransform to the respective beat signals for the channels Ch₁ to Ch_(M)(shown in the lower graph of FIG. 25) that are stored in the memory 531.In the present specification, the amplitude of a piece of complex numberdata after the Fourier transform is referred to as “signal intensity”.The reception intensity calculation section 532 converts the complexnumber data of a reception signal from one of the plurality of antennaelements, or a sum of the complex number data of all reception signalsfrom the plurality of antenna elements, into a frequency spectrum. Inthe resultant spectrum, beat frequencies corresponding to respectivepeak values, which are indicative of presence and distance of targets(preceding vehicles), can be detected. Taking a sum of the complexnumber data of the reception signals from all antenna elements willallow the noise components to average out, whereby the S/N ratio isimproved.

In the case where there is one target, i.e., one preceding vehicle, asshown in FIG. 26, the Fourier transform will produce a spectrum havingone peak value in a period of increasing frequency (the “ascent” period)and one peak value in a period of decreasing frequency (“the descent”period). The beat frequency of the peak value in the “ascent” period isdenoted by “fu”, whereas the beat frequency of the peak value in the“descent” period is denoted by “fd”.

From the signal intensities of beat frequencies, the reception intensitycalculation section 532 detects any signal intensity that exceeds apredefined value (threshold value), thus determining the presence of atarget. Upon detecting a signal intensity peak, the reception intensitycalculation section 532 outputs the beat frequencies (fu, fd) of thepeak values to the distance detection section 533 and the velocitydetection section 534 as the frequencies of the object of interest. Thereception intensity calculation section 532 outputs informationindicating the frequency modulation width Δf to the distance detectionsection 533, and outputs information indicating the center frequency f0to the velocity detection section 534.

In the case where signal intensity peaks corresponding to plural targetsare detected, the reception intensity calculation section 532 findassociations between the ascents peak values and the descent peak valuesbased on predefined conditions. Peaks which are determined as belongingto signals from the same target are given the same number, and thus arefed to the distance detection section 533 and the velocity detectionsection 534.

When there are plural targets, after the Fourier transform, as manypeaks as there are targets will appear in the ascent portions and thedescent portions of the beat signal. In proportion to the distancebetween the radar and a target, the reception signal will become moredelayed and the reception signal in FIG. 25 will shift more toward theright. Therefore, a beat signal will have a greater frequency as thedistant between the target and the radar increases.

Based on the beat frequencies fu and fd which are input from thereception intensity calculation section 532, the distance detectionsection 533 calculates a distance R through the equation below, andsupplies it to the target link processing section 537.

R={c·T/(2·Δf)}·{(fu+fd)/2}

Moreover, based on the beat frequencies fu and fd being input from thereception intensity calculation section 532, the velocity detectionsection 534 calculates a relative velocity V through the equation below,and supplies it to the target link processing section 537.

V={c/(2·f0)}·{(fu−fd)/2}

In the equation which calculates the distance R and the relativevelocity V, c is velocity of light, and T is the modulation period.

Note that the lower limit resolution of distance R is expressed asc/(2Δf). Therefore, as Δf increases, the resolution of distance Rincreases. In the case where the frequency f0 is in the 76 GHz band,when Δf is set on the order of 660 megahertz (MHz), the resolution ofdistance R will be on the order of 0.23 meters (m), for example.Therefore, if two preceding vehicles are traveling abreast of eachother, it may be difficult with the FMCW method to identify whetherthere is one vehicle or two vehicles. In such a case, it might bepossible to run an algorithm for direction-of-arrival estimation thathas an extremely high angular resolution to separate between theazimuths of the two preceding vehicles and enable detection.

By utilizing phase differences between signals from the antenna elements11 ₁, 11 ₂, . . . , 11 _(M), the DBF processing section 535 allows theincoming complex data corresponding to the respective antenna elements,which has been Fourier transformed with respect to the time axis, to beFourier transformed with respect to the direction in which the antennaelements are arrayed. Then, the DBF processing section 535 calculatesspatial complex number data indicating the spectrum intensity for eachangular channel as determined by the angular resolution, and outputs itto the azimuth detection section 536 for the respective beatfrequencies.

The azimuth detection section 536 is provided for the purpose ofestimating the azimuth of a preceding vehicle. Among the values ofspatial complex number data that has been calculated for the respectivebeat frequencies, the azimuth detection section 536 chooses an angle θthat takes the largest value, and outputs it to the target linkprocessing section 537 as the azimuth at which an object of interestexists.

Note that the method of estimating the angle θ indicating the directionof arrival of an arriving wave is not limited to this example. Variousalgorithms for direction-of-arrival estimation that have been mentionedearlier can be employed.

The target link processing section 537 calculates absolute values of thedifferences between the respective values of distance, relativevelocity, and azimuth of the object of interest as calculated in thecurrent cycle and the respective values of distance, relative velocity,and azimuth of the object of interest as calculated 1 cycle before,which are read from the memory 531. Then, if the absolute value of eachdifference is smaller than a value which is defined for the respectivevalue, the target link processing section 537 determines that the targetthat was detected 1 cycle before and the target detected in the currentcycle are an identical target. In that case, the target link processingsection 537 increments the count of target link processes, which is readfrom the memory 531, by one.

If the absolute value of a difference is greater than predetermined, thetarget link processing section 537 determines that a new object ofinterest has been detected. The target link processing section 537stores the respective values of distance, relative velocity, and azimuthof the object of interest as calculated in the current cycle and alsothe count of target link processes for that object of interest to thememory 531.

In the signal processing circuit 560, the distance to the object ofinterest and its relative velocity can be detected by using a spectrumwhich is obtained through a frequency analysis of beat signals, whichare signals generated based on received reflected waves.

The matrix generation section 538 generates a spatial covariance matrixby using the respective beat signals for the channels Ch₁ to Ch_(M)(lower graph in FIG. 25) stored in the memory 531. In the spatialcovariance matrix of Math. 4, each component is the value of a beatsignal which is expressed in terms of real and imaginary parts. Thematrix generation section 538 further determines eigenvalues of thespatial covariance matrix Rxx, and inputs the resultant eigenvalueinformation to the arriving wave estimation unit AU.

When a plurality of signal intensity peaks corresponding to pluralobjects of interest have been detected, the reception intensitycalculation section 532 numbers the peak values respectively in theascent portion and in the descent portion, beginning from those withsmaller frequencies first, and output them to the target outputprocessing section 539. In the ascent and descent portions, peaks of anyidentical number correspond to the same object of interest. Theidentification numbers are to be regarded as the numbers assigned to theobjects of interest. For simplicity of illustration, a leader line fromthe reception intensity calculation section 532 to the target outputprocessing section 539 is conveniently omitted from FIG. 24.

When the object of interest is a structure ahead, the target outputprocessing section 539 outputs the identification number of that objectof interest as indicating a target. When receiving results ofdetermination concerning plural objects of interest, such that all ofthem are structures ahead, the target output processing section 539outputs the identification number of an object of interest that is inthe lane of the driver's vehicle as the object position informationindicating where a target is. Moreover, When receiving results ofdetermination concerning plural objects of interest, such that all ofthem are structures ahead and that two or more objects of interest arein the lane of the driver's vehicle, the target output processingsection 539 outputs the identification number of an object of interestthat is associated with the largest count of target being read from thelink processes memory 531 as the object position information indicatingwhere a target is.

Referring back to FIG. 23, an example where the onboard radar system 510is incorporated in the exemplary construction shown in FIG. 23 will bedescribed. The image processing circuit 720 acquires information of anobject from the video, and detects target position information from theobject information. For example, the image processing circuit 720 isconfigured to estimate distance information of an object by detectingthe depth value of an object within an acquired video, or detect sizeinformation and the like of an object from characteristic amounts in thevideo, thus detecting position information of the object.

The selection circuit 596 selectively feeds position information whichis received from the signal processing circuit 560 or the imageprocessing circuit 720 to the travel assistance electronic controlapparatus 520. For example, the selection circuit 596 compares a firstdistance, i.e., the distance from the driver's vehicle to a detectedobject as contained in the object position information from the signalprocessing circuit 560, against a second distance, i.e., the distancefrom the driver's vehicle to the detected object as contained in theobject position information from the image processing circuit 720, anddetermines which is closer to the driver's vehicle. For example, basedon the result of determination, the selection circuit 596 may select theobject position information which indicates a closer distance to thedriver's vehicle, and output it to the travel assistance electroniccontrol apparatus 520. If the result of determination indicates thefirst distance and the second distance to be of the same value, theselection circuit 596 may output either one, or both of them, to thetravel assistance electronic control apparatus 520.

If information indicating that there is no prospective target is inputfrom the reception intensity calculation section 532, the target outputprocessing section 539 (FIG. 24) outputs zero, indicating that there isno target, as the object position information. Then, on the basis of theobject position information from the target output processing section539, through comparison against a predefined threshold value, theselection circuit 596 chooses either the object position informationfrom the signal processing circuit 560 or the object positioninformation from the image processing circuit 720 to be used.

Based on predefined conditions, the travel assistance electronic controlapparatus 520 having received the position information of a precedingobject from the object detection apparatus 570 performs control to makethe operation safer or easier for the driver who is driving the driver'svehicle, in accordance with the distance and size indicated by theobject position information, the velocity of the driver's vehicle, roadsurface conditions such as rainfall, snowfall or clear weather, or otherconditions. For example, if the object position information indicatesthat no object has been detected, the travel assistance electroniccontrol apparatus 520 may send a control signal to an acceleratorcontrol circuit 526 to increase speed up to a predefined velocity,thereby controlling the accelerator control circuit 526 to make anoperation that is equivalent to stepping on the accelerator pedal.

In the case where the object position information indicates that anobject has been detected, if it is found to be at a predetermineddistance from the driver's vehicle, the travel assistance electroniccontrol apparatus 520 controls the brakes via a brake control circuit524 through a brake-by-wire construction or the like. In other words, itmakes an operation of decreasing the velocity to maintain a constantvehicular gap. Upon receiving the object position information, thetravel assistance electronic control apparatus 520 sends a controlsignal to an alarm control circuit 522 so as to control lampillumination or control audio through a loudspeaker which is providedwithin the vehicle, so that the driver is informed of the nearing of apreceding object. Upon receiving object position information including aspatial distribution of preceding vehicles, the travel assistanceelectronic control apparatus 520 may, if the traveling velocity iswithin a predefined range, automatically make the steering wheel easierto operate to the right or left, or control the hydraulic pressure onthe steering wheel side so as to force a change in the direction of thewheels, thereby providing assistance in collision avoidance with respectto the preceding object.

The object detection apparatus 570 may be arranged so that, if a pieceof object position information which was being continuously detected bythe selection circuit 596 for a while in^(L) the previous detectioncycle but which is not detected in the current detection cycle becomesassociated with a piece of object position information from acamera-detected video indicating a preceding object, then continuedtracking is chosen, and object position information from the signalprocessing circuit 560 is output with priority.

An exemplary specific construction and an exemplary operation for theselection circuit 596 to make a selection between the outputs from thesignal processing circuit 560 and the image processing circuit 720 aredisclosed in the specification of U.S. Pat. No. 8,446,312, thespecification of U.S. Pat. No. 8,730,096, and the specification of U.S.Pat. No. 8,730,099. The entire disclosure thereof is incorporated hereinby reference.

[First Variant]

In the radar system for onboard use of the above Application Example,the (sweep) condition for a single instance of FMCW (Frequency ModulatedContinuous Wave) frequency modulation, i.e., a time span required forsuch a modulation (sweep time), is e.g. 1 millisecond, although thesweep time could be shortened to about 100 microseconds.

However, in order to realize such a rapid sweep condition, not only theconstituent elements involved in the radiation of a transmission wave,but also the constituent elements involved in the reception under thatsweep condition must also be able to rapidly operate. For example, anA/D converter 587 (FIG. 24) which rapidly operates under that sweepcondition will be needed. The sampling frequency of the A/D converter587 may be 10 MHz, for example. The sampling frequency may be fasterthan 10 MHz.

In the present variant, a relative velocity with respect to a target iscalculated without utilizing any Doppler shift-based frequencycomponent. In this variant, the sweep time is Tm=100 microseconds, whichis very short. The lowest frequency of a detectable beat signal, whichis 1/Tm, equals 10 kHz in this case. This would correspond to a Dopplershift of a reflected wave from a target which has a relative velocity ofapproximately 20 m/second. In other words, so long as one relies on aDoppler shift, it would be impossible to detect relative velocities thatare equal to or smaller than this. Thus, a method of calculation whichis different from a Doppler shift-based method of calculation ispreferably adopted.

As an example, this variant illustrates a process that utilizes a signal(upbeat signal) representing a difference between a transmission waveand a reception wave which is obtained in an upbeat (ascent) portionwhere the transmission wave increases in frequency. A single sweep timeof FMCW is 100 microseconds, and its waveform is a sawtooth shape whichis composed only of an upbeat portion. In other words, in this variant,the signal wave which is generated by the triangular wave/CW wavegeneration circuit 581 has a sawtooth shape. The sweep width infrequency is 500 MHz. Since no peaks are to be utilized that areassociated with Doppler shifts, the process is not one that generates anupbeat signal and a downbeat signal to utilize the peaks of both, butwill rely on only one of such signals. Although a case of utilizing anupbeat signal will be illustrated herein, a similar process can also beperformed by using a downbeat signal.

The A/D converter 587 (FIG. 24) samples each upbeat signal at a samplingfrequency of 10 MHz, and outputs several hundred pieces of digital data(hereinafter referred to as “sampling data”). The sampling data isgenerated based on upbeat signals after a point in time where areception wave is obtained and until a point in time at which atransmission wave completes transmission, for example. Note that theprocess may be ended as soon as a certain number of pieces of samplingdata are obtained.

In this variant, 128 upbeat signals are transmitted/received in series,for each of which some several hundred pieces of sampling data areobtained. The number of upbeat signals is not limited to 128. It may be256, or 8. An arbitrary number may be selected depending on the purpose.

The resultant sampling data is stored to the memory 531. The receptionintensity calculation section 532 applies a two-dimensional fast Fouriertransform (FFT) to the sampling data. Specifically, first, for each ofthe sampling data pieces that have been obtained through a single sweep,a first FFT process (frequency analysis process) is performed togenerate a power spectrum. Next, the velocity detection section 534performs a second FFT process for the processing results that have beencollected from all sweeps.

When the reflected waves are from the same target, peak components inthe power spectrum to be detected in each sweep period will be of thesame frequency. On the other hand, for different targets, the peakcomponents will differ in frequency. Through the first FFT process,plural targets that are located at different distances can be separated.

In the case where a relative velocity with respect to a target isnon-zero, the phase of the upbeat signal changes slightly from sweep tosweep. In other words, through the second FFT process, a power spectrumwhose elements are the data of frequency components that are associatedwith such phase changes will be obtained for the respective results ofthe first FFT process.

The reception intensity calculation section 532 extracts peak values inthe second power spectrum above, and sends them to the velocitydetection section 534.

The velocity detection section 534 determines a relative velocity fromthe phase changes. For example, suppose that a series of obtained upbeatsignals undergo phase changes by every phase θ [RXd]. Assuming that thetransmission wave has an average wavelength λ, this means there is aλ/(4π/θ) change in distance every time an upbeat signal is obtained.Since this change has occurred over an interval of upbeat signaltransmission Tm (=100 microseconds), the relative velocity is determinedto be {λ/(4π/θ)}/Tm.

Through the above processes, a relative velocity with respect to atarget as well as a distance from the target can be obtained.

[Second Variant]

The radar system 510 is able to detect a target by using a continuouswave(s) CW of one or plural frequencies. This method is especiallyuseful in an environment where a multitude of reflected waves impinge onthe radar system 510 from still objects in the surroundings, e.g., whenthe vehicle is in a tunnel.

The radar system 510 has an antenna array for reception purposes,including five channels of independent reception elements. In such aradar system, the azimuth-of-arrival estimation for incident reflectedwaves is only possible if there are four or fewer reflected waves thatare simultaneously incident. In an FMCW-type radar, the number ofreflected waves to be simultaneously subjected to an azimuth-of-arrivalestimation can be reduced by exclusively selecting reflected waves froma specific distance. However, in an environment where a large number ofstill objects exist in the surroundings, e.g., in a tunnel, it is as ifthere were a continuum of objects to reflect radio waves; therefore,even if one narrows down on the reflected waves based on distance, thenumber of reflected waves may still not be equal to or smaller thanfour. However, any such still object in the surroundings will have anidentical relative velocity with respect to the driver's vehicle, andthe relative velocity will be greater than that associated with anyother vehicle that is traveling ahead. On this basis, such still objectscan be distinguished from any other vehicle based on the magnitudes ofDoppler shifts.

Therefore, the radar system 510 performs a process of: radiatingcontinuous waves CW of plural frequencies; and, while ignoring Dopplershift peaks that correspond to still objects in the reception signals,detecting a distance by using a Doppler shift peak(s) of any smallershift amount(s). Unlike in the FMCW method, in the CW method, afrequency difference between a transmission wave and a reception wave isascribable only to a Doppler shift. In other words, any peak frequencythat appears in a beat signal is ascribable only to a Doppler shift.

In the description of this variant, too, a continuous wave to be used inthe CW method will be referred to as a “continuous wave CW”. Asdescribed above, a continuous wave CW has a constant frequency; that is,it is unmodulated.

Suppose that the radar system 510 has radiated a continuous wave CW of afrequency fp, and detected a reflected wave of a frequency fq that hasbeen reflected off a target. The difference between the transmissionfrequency fp and the reception frequency fq is called a Dopplerfrequency, which approximates to fp−fq=2·Vr·fp/c. Herein, Vr is arelative velocity between the radar system and the target, and c is thevelocity of light. The transmission frequency fp, the Doppler frequency(fp−fq), and the velocity of light c are known. Therefore, from thisequation, the relative velocity Vr=(fp−fq)·c/2fp can be determined. Thedistance to the target is calculated by utilizing phase information aswill be described later.

In order to detect a distance to a target by using continuous waves CW,a 2 frequency CW method is adopted. In the 2 frequency CW method,continuous waves CW of two frequencies which are slightly apart areradiated each for a certain period, and their respective reflected wavesare acquired. For example, in the case of using frequencies in the 76GHz band, the difference between the two frequencies would be severalhundred kHz. As will be described later, it is more preferable todetermine the difference between the two frequencies while taking intoaccount the minimum distance at which the radar used is able to detect atarget.

Suppose that the radar system 510 has sequentially radiated continuouswaves CW of frequencies fp1 and fp2 (fp1<fp2), and that the twocontinuous waves CW have been reflected off a single target, resultingin reflected waves of frequencies fq1 and fq2 being received by theradar system 510.

Based on the continuous wave CW of the frequency fp1 and the reflectedwave (frequency fq1) thereof, a first Doppler frequency is obtained.Based on the continuous wave CW of the frequency fp2 and the reflectedwave (frequency fq2) thereof, a second Doppler frequency is obtained.The two Doppler frequencies have substantially the same value. However,due to the difference between the frequencies fp1 and fp2, the complexsignals of the respective reception waves differ in phase. By utilizingthis phase information, a distance (range) to the target can becalculated.

Specifically, the radar system 510 is able to determine the distance Ras R=c·Δϕ/4π(fp2−fp1). Herein, Δϕ denotes the phase difference betweentwo beat signals, i.e., beat signal fb1 which is obtained as adifference between the continuous wave CW of the frequency fp1 and thereflected wave (frequency fq1) thereof and beat signal fb2 which isobtained as a difference between the continuous wave CW of the frequencyfp2 and the reflected wave (frequency fq2) thereof. The method ofidentifying the frequency fb1 and fb2 of the respective beat signals isidentical to that in the aforementioned instance of a beat signal from acontinuous wave CW of a single frequency.

Note that a relative velocity Vr under the 2 frequency CW method isdetermined as follows.

Vr=fb1·c/2·fp1 or Vr=fb2·c/2·fp2

Moreover, the range in which a distance to a target can be uniquelyidentified is limited to the range defined by Rmax<c/2(fp2−fp1). Thereason is that beat signals resulting from a reflected wave from anyfarther target would produce a Δϕ which is greater than 2π, such thatthey are indistinguishable from beat signals associated with targets atcloser positions. Therefore, it is more preferable to adjust thedifference between the frequencies of the two continuous waves CW sothat Rmax becomes greater than the minimum detectable distance of theradar. In the case of a radar whose minimum detectable distance is 100m, fp2−fp1 may be made e.g. 1.0 MHz. In this case, Rmax=150 m, so that asignal from any target from a position beyond Rmax is not detected. Inthe case of mounting a radar which is capable of detection up to 250 m,fp2−fp1 may be made e.g. 500 kHz. In this case, Rmax=300 m, so that asignal from any target from a position beyond Rmax is not detected,either. In the case where the radar has both of an operation mode inwhich the minimum detectable distance is 100 m and the horizontalviewing angle is 120 degrees and an operation mode in which the minimumdetectable distance is 250 m and the horizontal viewing angle is 5degrees, it is preferable to switch the fp2−fp1 value be 1.0 MHz and 500kHz for operation in the respective operation modes.

A detection approach is known which, by transmitting continuous waves CWat N different frequencies (where N is an integer of 3 or more), andutilizing phase information of the respective reflected waves, detects adistance to each target. Under this detection approach, distance can beproperly recognized up to N−1 targets. As the processing to enable this,a fast Fourier transform (FFT) is used, for example. Given N=64 or 128,an FFT is performed for sampling data of a beat signal as a differencebetween a transmission signal and a reception signal for each frequency,thus obtaining a frequency spectrum (relative velocity). Thereafter, atthe frequency of the CW wave, a further FFT is performed for peaks ofthe same frequency, thus to derive distance information.

Hereinafter, this will be described more specifically.

For ease of explanation, first, an instance will be described wheresignals of three frequencies f1, f2 and f3 are transmitted while beingswitched over time. It is assumed that f1>f2>f3, and f1−f2=f2−f3=Δf. Atransmission time Δt is assumed for the signal wave for each frequency.FIG. 28 shows a relationship between three frequencies f1, f2 and f3.

Via the transmission antenna Tx, the triangular wave/CW wave generationcircuit 581 (FIG. 24) transmits continuous waves CW of frequencies f1,f2 and f3, each lasting for the time Δt. The reception antennas Rxreceive reflected waves resulting by the respective continuous waves CWbeing reflected off one or plural targets.

Each mixer 584 mixes a transmission wave and a reception wave togenerate a beat signal. The A/D converter 587 converts the beat signal,which is an analog signal, into several hundred pieces of digital data(sampling data), for example.

Using the sampling data, the reception intensity calculation section 532performs FFT computation. Through the FFT computation, frequencyspectrum information of reception signals is obtained for the respectivetransmission frequencies f1, f2 and f3.

Thereafter, the reception intensity calculation section 532 separatespeak values from the frequency spectrum information of the receptionsignals. The frequency of any peak value which is predetermined orgreater is in proportion to a relative velocity with respect to atarget. Separating a peak value(s) from the frequency spectruminformation of reception signals is synonymous with separating one orplural targets with different relative velocities.

Next, with respect to each of the transmission frequencies f1 to f3, thereception intensity calculation section 532 measures spectruminformation of peak values of the same relative velocity or relativevelocities within a predefined range.

Now, consider a scenario where two targets A and B exist which haveabout the same relative velocity but are at respectively differentdistances. A transmission signal of the frequency f1 will be reflectedfrom both of targets A and B to result in reception signals beingobtained. The reflected waves from targets A and B will result insubstantially the same beat signal frequency. Therefore, the powerspectra at the Doppler frequencies of the reception signals,corresponding to their relative velocities, are obtained as a syntheticspectrum F1 into which the power spectra of two targets A and B havebeen merged.

Similarly, for each of the frequencies f2 and f3, the power spectra atthe Doppler frequencies of the reception signals, corresponding to theirrelative velocities, are obtained as a synthetic spectrum F1 into whichthe power spectra of two targets A and B have been merged.

FIG. 29 shows a relationship between synthetic spectra F1 to F3 on acomplex plane. In the directions of the two vectors composing each ofthe synthetic spectra F1 to F3, the right vector corresponds to thepower spectrum of a reflected wave from target A; i.e., vectors f1A, f2Aand f3A, in FIG. 29. On the other hand, in the directions of the twovectors composing each of the synthetic spectra F1 to F3, the leftvector corresponds to the power spectrum of a reflected wave from targetB; i.e., vectors f1B, f2B and f3B in FIG. 29.

Under a constant difference Δf between the transmission frequencies, thephase difference between the reception signals corresponding to therespective transmission signals of the frequencies f1 and f2 is inproportion to the distance to a target. Therefore, the phase differencebetween the vectors f1A and f2A and the phase difference between thevectors f2A and f3A are of the same value θA, this phase difference θAbeing in proportion to the distance to target A. Similarly, the phasedifference between the vectors f1B and f2B and the phase differencebetween the vectors f2B and f3B are of the same value θB, this phasedifference θB being in proportion to the distance to target B.

By using a well-known method, the respective distances to targets A andB can be determined from the synthetic spectra F1 to F3 and thedifference Δf between the transmission frequencies. This technique isdisclosed in U.S. Pat. No. 6703967, for example. The entire disclosureof this publication is incorporated herein by reference.

Similar processing is also applicable when the transmitted signals havefour or more frequencies.

Note that, before transmitting continuous waves CW at N differentfrequencies, a process of determining the distance to and relativevelocity of each target may be performed by the 2 frequency CW method.Then, under predetermined conditions, this process may be switched to aprocess of transmitting continuous waves CW at N different frequencies.For example, FFT computation may be performed by using the respectivebeat signals at the two frequencies, and if the power spectrum of eachtransmission frequency undergoes a change over time of 30% or more, theprocess may be switched. The amplitude of a reflected wave from eachtarget undergoes a large change over time due to multipath influencesand the like. When there exists a change of a predetermined magnitude orgreater, it may be considered that plural targets may exist.

Moreover, the CW method is known to be unable to detect a target whenthe relative velocity between the radar system and the target is zero,i.e., when the Doppler frequency is zero. However, when a pseudo Dopplersignal is determined by the following methods, for example, it ispossible to detect a target by using that frequency.

(Method 1) A mixer that causes a certain frequency shift in the outputof a receiving antenna is added. By using a transmission signal and areception signal with a shifted frequency, a pseudo Doppler signal canbe obtained.

(Method 2) A variable phase shifter to introduce phase changescontinuously over time is inserted between the output of a receivingantenna and a mixer, thus adding a pseudo phase difference to thereception signal. By using a transmission signal and a reception signalwith an added phase difference, a pseudo Doppler signal can be obtained.

An example of specific construction and operation of inserting avariable phase shifter to generate a pseudo Doppler signal under Method2 is disclosed in Japanese Laid-Open Patent Publication No. 2004-257848.The entire disclosure of this publication is incorporated herein byreference.

When targets with zero or very little relative velocity need to bedetected, the aforementioned processes of generating a pseudo Dopplersignal may be adopted, or the process may be switched to a targetdetection process under the FMCW method.

Next, with reference to FIG. 30, a procedure of processing to beperformed by the object detection apparatus 570 of the onboard radarsystem 510 will be described.

The example below will illustrate a case where continuous waves CW aretransmitted at two different frequencies fp1 and fp2 (fp1<fp2), and thephase information of each reflected wave is utilized to respectivelydetect a distance with respect to a target.

FIG. 30 is a flowchart showing the procedure of a process of determiningrelative velocity and distance according to this variant.

At step S41, the triangular wave/CW wave generation circuit 581generates two continuous waves CW of frequencies which are slightlyapart, i.e., frequencies fp1 and fp2.

At step S42, the transmission antenna Tx and the reception antennas Rxperform transmission/reception of the generated series of continuouswaves CW. Note that the process of step S41 and the process of step S42are to be performed in parallel fashion respectively by the triangularwave/CW wave generation circuit 581 and the transmission antennaTx/reception antenna Rx, rather than step S42 following only aftercompletion of step S41.

At step S43, each mixer 584 generates a difference signal by utilizingeach transmission wave and each reception wave, whereby two differencesignals are obtained. Each reception wave is inclusive of a receptionwave emanating from a still object and a reception wave emanating from atarget. Therefore, next, a process of identifying frequencies to beutilized as the beat signals is performed. Note that the process of stepS41, the process of step S42, and the process of step S43 are to beperformed in parallel fashion by the triangular wave/CW wave generationcircuit 581, the transmission antenna Tx/reception antenna Rx, and themixers 584, rather than step S42 following only after completion of stepS41, or step S43 following only after completion of step S42.

At step S44, for each of the two difference signals, the objectdetection apparatus 570 identifies certain peak frequencies to befrequencies fb1 and fb2 of beat signals, such that these frequencies areequal to or smaller than a frequency which is predefined as a thresholdvalue and yet they have amplitude values which are equal to or greaterthan a predetermined amplitude value, and that the difference betweenthe two frequencies is equal to or smaller than a predetermined value.

At step S45, based on one of the two beat signal frequencies identified,the reception intensity calculation section 532 detects a relativevelocity. The reception intensity calculation section 532 calculates therelative velocity according to Vr=fb1·c/2·fp1, for example. Note that arelative velocity may be calculated by utilizing each of the two beatsignal frequencies, which will allow the reception intensity calculationsection 532 to verify whether they match or not, thus enhancing theprecision of relative velocity calculation.

At step S46, the reception intensity calculation section 532 determinesa phase difference Δϕ between two beat signals fb1 and fb2, anddetermines a distance R=c·Δϕ/4π(fp2−fp1) to the target.

Through the above processes, the relative velocity and distance to atarget can be detected.

Note that continuous waves CW may be transmitted at N differentfrequencies (where N is 3 or more), and by utilizing phase informationof the respective reflected wave, distances to plural targets which areof the same relative velocity but at different positions may bedetected.

In addition to the radar system 510, the vehicle 500 described above mayfurther include another radar system. For example, the vehicle 500 mayfurther include a radar system having a detection range toward the rearor the sides of the vehicle body. In the case of incorporating a radarsystem having a detection range toward the rear of the vehicle body, theradar system may monitor the rear, and if there is any danger of havinganother vehicle bump into the rear, make a response by issuing an alarm,for example. In the case of incorporating a radar system having adetection range toward the sides of the vehicle body, the radar systemmay monitor an adjacent lane when the driver's vehicle changes its lane,etc., and make a response by issuing an alarm or the like as necessary.

The applications of the above-described radar system 510 are not limitedto onboard use only. Rather, the radar system 510 may be used as sensorsfor various purposes. For example, it may be used as a radar formonitoring the surroundings of a house or any other building.Alternatively, it may be used as a sensor for detecting the presence orabsence of a person at a specific indoor place, or whether or not such aperson is undergoing any motion, etc., without utilizing any opticalimages.

[Supplementary Details of Processing]

Other embodiments will be described in connection with the 2 frequencyCW or FMCW techniques for array antennas as described above. Asdescribed earlier, in the example of FIG. 24, the reception intensitycalculation section 532 applies a Fourier transform to the respectivebeat signals for the channels Ch₁ to Ch_(M) (lower graph in FIG. 25)stored in the memory 531. These beat signals are complex signals, inorder that the phase of the signal of computational interest beidentified. This allows the direction of an arriving wave to beaccurately identified. In this case, however, the computational load forFourier transform increases, thus calling for a larger-scaled circuit.

In order to solve this problem, a scalar signal may be generated as abeat signal. For each of a plurality of beat signals that have beengenerated, two complex Fourier transforms may be performed with respectto the spatial axis direction, which conforms to the antenna array, andto the time axis direction, which conforms to the lapse of time, thus toobtain results of frequency analysis. As a result, with only a smallamount of computation, beam formation can eventually be achieved so thatdirections of arrival of reflected waves can be identified, wherebyresults of frequency analysis can be obtained for the respective beams.As a patent document related to the present disclosure, the entiredisclosure of the specification of U.S. Pat. No. 6,339,395 isincorporated herein by reference.

[Optical Sensor, e.g., Camera, and Millimeter Wave Radar]

Next, a comparison between the above-described array antenna andconventional antennas, as well as an exemplary application in which bothof the present array antenna and an optical sensor (e.g., a camera) areutilized, will be described. Note that LIDAR or the like may be employedas the optical sensor.

A millimeter wave radar is able to directly detect a distance (range) toa target and a relative velocity thereof. Another characteristic is thatits detection performance is not much deteriorated in the nighttime(including dusk), or in bad weather, e.g., rainfall, fog, or snowfall.On the other hand, it is believed that it is not just as easy for amillimeter wave radar to take a two-dimensional grasp of a target as itis for a camera. On the other hand, it is relatively easy for a camerato take a two-dimensional grasp of a target and recognize its shape.However, a camera may not be able to image a target in nighttime or badweather, which presents a considerable problem. This problem isparticularly outstanding when droplets of water have adhered to theportion through which to ensure lighting, or the eyesight is narrowed bya fog. This problem similarly exists for LIDAR or the like, which alsopertains to the realm of optical sensors.

In these years, in answer to increasing demand for safer vehicleoperation, driver assist systems for preventing collisions or the likeare being developed. A driver assist system acquires an image in thedirection of vehicle travel with a sensor such as a camera or amillimeter wave radar, and when any obstacle is recognized that ispredicted to hinder vehicle travel, brakes or the like are automaticallyapplied to prevent collisions or the like. Such a function of collisionavoidance is expected to operate normally, even in nighttime or badweather.

Hence, driver assist systems of a so-called fusion construction aregaining prevalence, where, in addition to a conventional optical sensorsuch as a camera, a millimeter wave radar is mounted as a sensor, thusrealizing a recognition process that takes advantage of both. Such adriver assist system will be discussed later.

On the other hand, higher and higher functions are being required of themillimeter wave radar itself. A millimeter wave radar for onboard usemainly uses electromagnetic waves of the 76 GHz band. The antenna powerof its antenna is restricted to below a certain level under eachcountry's law or the like. For example, it is restricted to 0.01 W orbelow in Japan. Under such restrictions, a millimeter wave radar foronboard use is expected to satisfy the required performance that, forexample, its detection range is 200 m or more; the antenna size is 60mm×60 mm or less; its horizontal detection angle is 90 degrees or more;its range resolution is 20 cm or less; it is capable of short-rangedetection within 10 m; and so on. Conventional millimeter wave radarshave used microstrip lines as waveguides, and patch antennas as antennas(hereinafter, these will both be referred to as “patch antennas”).However, with a patch antenna, it has been difficult to attain theaforementioned performance.

By using a slot array antenna to which the technique of the presentdisclosure is applied, the inventors have successfully achieved theaforementioned performance. As a result, a millimeter wave radar hasbeen realized which is smaller in size, more efficient, andhigher-performance than are conventional patch antennas and the like. Inaddition, by combining this millimeter wave radar and an optical sensorsuch as a camera, a small-sized, highly efficient, and high-performancefusion apparatus has been realized which has existed never before. Thiswill be described in detail below.

FIG. 31 is a diagram concerning a fusion apparatus in a vehicle 500, thefusion apparatus including an onboard camera system 700 and a radarsystem 510 (hereinafter referred to also as the millimeter wave radar510) having a slot array antenna to which the technique of the presentdisclosure is applied. With reference to this figure, variousembodiments will be described below.

[Installment of Millimeter Wave Radar within Vehicle Room]

A conventional patch antenna-based millimeter wave radar 510′ is placedbehind and inward of a grill 512 which is at the front nose of avehicle. An electromagnetic wave that is radiated from an antenna goesthrough the apertures in the grill 512, and is radiated ahead of thevehicle 500. In this case, no dielectric layer, e.g., glass, exists thatdecays or reflects electromagnetic wave energy, in the region throughwhich the electromagnetic wave passes. As a result, an electromagneticwave that is radiated from the patch antenna-based millimeter wave radar510′ reaches over a long range, e.g., to a target which is 150 m orfarther away. By receiving with the antenna the electromagnetic wavereflected therefrom, the millimeter wave radar 510′ is able to detect atarget. In this case, however, since the antenna is placed behind andinward of the grill 512 of the vehicle, the radar may be broken when thevehicle collides into an obstacle. Moreover, it may be soiled with mudor the like in rain, etc., and the soil that has adhered to the antennamay hinder radiation and reception of electromagnetic waves.

Similarly to the conventional manner, the millimeter wave radar 510incorporating a slot array antenna according to an embodiment of thepresent disclosure may be placed behind the grill 512, which is locatedat the front nose of the vehicle (not shown). This allows the energy ofthe electromagnetic wave to be radiated from the antenna to be utilizedby 100%, thus enabling long-range detection beyond the conventionallevel, e.g., detection of a target which is at a distance of 250 m ormore.

Furthermore, the millimeter wave radar 510 according to an embodiment ofthe present disclosure can also be placed within the vehicle room, i.e.,inside the vehicle. In that case, the millimeter wave radar 510 isplaced inward of the windshield 511 of the vehicle, to fit in a spacebetween the windshield 511 and a face of the rearview mirror (not shown)that is opposite to its specular surface. On the other hand, theconventional patch antenna-based millimeter wave radar 510′ cannot beplaced inside the vehicle room mainly for the two following reasons. Afirst reason is its large size, which prevents itself from beingaccommodated within the space between the windshield 511 and therearview mirror. A second reason is that an electromagnetic wave that isradiated ahead reflects off the windshield 511 and decays due todielectric loss, thus becoming unable to travel the desired distance. Asa result, if a conventional patch antenna-based millimeter wave radar isplaced within the vehicle room, only targets which are 100 m ahead orless can be detected, for example. On the other hand, a millimeter waveradar according to an embodiment of the present disclosure is able todetect a target which is at a distance of 200 m or more, despitereflection or decay at the windshield 511. This performance isequivalent to, or even greater than, the case where a conventional patchantenna-based millimeter wave radar is placed outside the vehicle room.

[Fusion Construction Based on Millimeter Wave Radar and Camera, etc.,Being Placed within Vehicle Room]

Currently, an optical imaging device such as a CCD camera is used as themain sensor in many a driver assist system (Driver Assist System).Usually, a camera or the like is placed within the vehicle room, inwardof the windshield 511, in order to account for unfavorable influences ofthe external environment, etc. In this context, in order to minimize theoptical effect of raindrops and the like, the camera or the like isplaced in a region which is swept by the wipers (not shown) but isinward of the windshield 511.

In recent years, due to needs for improved performance of a vehicle interms of e.g. automatic braking, there has been a desire for automaticbraking or the like that is guaranteed to work regardless of whateverexternal environment may exist. In this case, if the only sensor in thedriver assist system is an optical device such as a camera, a problemexists in that reliable operation is not guaranteed in nighttime or badweather. This has led to the need for a driver assist system thatincorporates not only an optical sensor (such as a camera) but also amillimeter wave radar, these being used for cooperative processing, sothat reliable operation is achieved even in nighttime or bad weather.

As described earlier, a millimeter wave radar incorporating the presentslot array antenna permits itself to be placed within the vehicle room,due to downsizing and remarkable enhancement in the efficiency of theradiated electromagnetic wave over that of a conventional patch antenna.By taking advantage of these properties, as shown in FIG. 31, themillimeter wave radar 510, which incorporates not only an optical sensor(onboard camera system) 700 such as a camera but also a slot arrayantenna according to the present disclosure, allows both to be placedinward of the windshield 511 of the vehicle 500. This has created thefollowing novel effects.

-   (1) It is easier to install the driver assist system on the vehicle    500. The conventional patch antenna-based millimeter wave radar 510′    has required a space behind the grill 512, which is at the front    nose, in order to accommodate the radar. Since this space may    include some sites that affect the structural design of the vehicle,    if the size of the radar device is changed, it may have been    necessary to reconsider the structural design. This inconvenience is    avoided by placing the millimeter wave radar within the vehicle    room.-   (2) Free from the influences of rain, nighttime, or other external    environment factors to the vehicle, more reliable operation can be    achieved. Especially, as shown in FIG. 32, by placing the millimeter    wave radar (onboard camera system) 510 and the onboard camera system    700 at substantially the same position within the vehicle room, they    can attain an identical field of view and line of sight, thus    facilitating the “matching process” which will be described later,    i.e., a process through which to establish that respective pieces of    target information captured by them actually come from an identical    object. On the other hand, if the millimeter wave radar 510′ were    placed behind the grill 512, which is at the front nose outside the    vehicle room, its radar line of sight L would differ from a radar    line of sight M of the case where it was placed within the vehicle    room, thus resulting in a large offset with the image to be acquired    by the onboard camera system 700.-   (3) Reliability of the millimeter wave radar device is improved. As    described above, since the conventional patch antenna-based    millimeter wave radar 510′ is placed behind the grill 512, which is    at the front nose, it is likely to gather soil, and may be broken    even in a minor collision accident or the like. For these reasons,    cleaning and functionality checks are always needed. Moreover, as    will be described below, if the position or direction of attachment    of the millimeter wave radar becomes shifted due to an accident or    the like, it is necessary to reestablish alignment with respect to    the camera. The chances of such occurrences are reduced by placing    the millimeter wave radar within the vehicle room, whereby the    aforementioned inconveniences are avoided.

In a driver assist system of such fusion construction, the opticalsensor, e.g., a camera, and the millimeter wave radar 510 incorporatingthe present slot array antenna may have an integrated construction,i.e., being in fixed position with respect to each other. In that case,certain relative positioning should be kept between the optical axis ofthe optical sensor such as a camera and the directivity of the antennaof the millimeter wave radar, as will be described later. When thisdriver assist system having an integrated construction is fixed withinthe vehicle room of the vehicle 500, the optical axis of the camera,etc., should be adjusted so as to be oriented in a certain directionahead of the vehicle. For these matters, see the specification of USPatent Application Publication No. 2015/0264230, the specification of USPatent Application Publication No. 2016/0264065, U.S. patent applicationSer. No. 15/248,141, U.S. patent application Ser. No. 15/248,149, andU.S. patent application Ser. No. 15/248,156, which are incorporatedherein by reference. Related techniques concerning the camera aredescribed in the specification of U.S. Pat. No. 7,355,524, and thespecification of U.S. Pat. No. 7,420,159, the entire disclosure of eachwhich is incorporated herein by reference.

Regarding placement of an optical sensor such as a camera and amillimeter wave radar within the vehicle room, see, for example, thespecification of U.S. Pat. No. 8,604,968, the specification of U.S. Pat.No. 8,614,640, and the specification of U.S. Pat. No. 7,978,122, theentire disclosure of each which is incorporated herein by reference.However, at the time when these patents were filed for, onlyconventional antennas with patch antennas were the known millimeter waveradars, and thus observation was not possible over sufficient distances.For example, the distance that is observable with a conventionalmillimeter wave radar is considered to be at most 100 m to 150 m.Moreover, when a millimeter wave radar is placed inward of thewindshield, the large radar size inconveniently blocks the driver'sfield of view, thus hindering safe driving. On the other hand, amillimeter wave radar incorporating a slot array antenna according to anembodiment of the present disclosure is capable of being placed withinthe vehicle room because of its small size and remarkable enhancement inthe efficiency of the radiated electromagnetic wave over that of aconventional patch antenna. This enables a long-range observation over200 m, while not blocking the driver's field of view.

[Adjustment of Position of Attachment between Millimeter Wave Radar andCamera, etc.,]

In the processing under fusion construction (which hereinafter may bereferred to as a “fusion process”), it is desired that an image which isobtained with a camera or the like and the radar information which isobtained with the millimeter wave radar map onto the same coordinatesystem because, if they differ as to position and target size,cooperative processing between both will be hindered.

This involves adjustment from the following three standpoints.

(1) The optical axis of the camera or the like and the antennadirectivity of the millimeter wave radar must have a certain fixedrelationship.

It is required that the optical axis of the camera or the like and theantenna directivity of the millimeter wave radar are matched.Alternatively, a millimeter wave radar may include two or moretransmission antennas and two or more reception antennas, thedirectivities of these antennas being intentionally made different.Therefore, it is necessary to guarantee that at least a certain knownrelationship exists between the optical axis of the camera or the likeand the directivities of these antennas.

In the case where the camera or the like and the millimeter wave radarhave the aforementioned integrated construction, i.e., being in fixedposition to each other, the relative positioning between the camera orthe like and the millimeter wave radar stays fixed. Therefore, theaforementioned requirements are satisfied with respect to such anintegrated construction. On the other hand, in a conventional patchantenna or the like, where the millimeter wave radar is placed behindthe grill 512 of the vehicle 500, the relative positioning between themis usually to be adjusted according to (2) below.

(2) A certain fixed relationship exists between an image acquired withthe camera or the like and radar information of the millimeter waveradar in an initial state (e.g., upon shipment) of having been attachedto the vehicle.

The positions of attachment of the optical sensor such as a camera andthe millimeter wave radar 510 or 510′ on the vehicle 500 will finally bedetermined in the following manner. At a predetermined position 800ahead of the vehicle 500, a chart to serve as a reference or a targetwhich is subject to observation by the radar (which will hereinafter bereferred to as, respectively, a “reference chart” and a “referencetarget”, and collectively as the “benchmark”) is accurately positioned.This is observed with an optical sensor such as a camera or with themillimeter wave radar 510. The observation information regarding theobserved benchmark is compared against previously-stored shapeinformation or the like of the benchmark, and the current offsetinformation is quantitated. Based on this offset information, by atleast one of the following means, the positions of attachment of anoptical sensor such as a camera and the millimeter wave radar 510 or510′ are adjusted or corrected. Any other means may also be employedthat can provide similar results.

(i) Adjust the positions of attachment of the camera and the millimeterwave radar so that the benchmark will come at a midpoint between thecamera and the millimeter wave radar. This adjustment may be done byusing a jig or tool, etc., which is separately provided.

(ii) Determine an offset amounts of the camera and the axis/directivityof the millimeter wave radar relative to the benchmark, and throughimage processing of the camera image and radar processing, correct forthese offset amounts in the axis/directivity.

What is to be noted is that, in the case where the optical sensor suchas a camera and the millimeter wave radar 510 incorporating a slot arrayantenna according to an embodiment of the present disclosure have anintegrated construction, i.e., being in fixed position to each other,adjusting an offset of either the camera or the radar with respect tothe benchmark will make the offset amount known for the other as well,thus making it unnecessary to check for the other's offset with respectto the benchmark.

Specifically, with respect to the onboard camera system 700, a referencechart may be placed at a predetermined position 750, and an image takenby the camera is compared against advance information indicating wherein the field of view of the camera the reference chart image is supposedto be located, thereby detecting an offset amount. Based on this, thecamera is adjusted by at least one of the above means (i) and (ii).Next, the offset amount which has been ascertained for the camera istranslated into an offset amount of the millimeter wave radar.Thereafter, an offset amount adjustment is made with respect to theradar information, by at least one of the above means (i) and (ii).

Alternatively, this may be performed on the basis of the millimeter waveradar 510. In other words, with respect to the millimeter wave radar510, a reference target may be placed at a predetermined position 800,and the radar information thereof is compared against advanceinformation indicating where in the field of view of the millimeter waveradar 510 the reference target is supposed to be located, therebydetecting an offset amount. Based on this, the millimeter wave radar 510is adjusted by at least one of the above means (i) and (ii). Next, theoffset amount which has been ascertained for the millimeter wave radaris translated into an offset amount of the camera. Thereafter, an offsetamount adjustment is made with respect to the image information obtainedby the camera, by at least one of the above means (i) and (ii).

(3) Even after an initial state of the vehicle, a certain relationshipis maintained between an image acquired with the camera or the like andradar information of the millimeter wave radar.

Usually, an image acquired with the camera or the like and radarinformation of the millimeter wave radar are supposed to be fixed in theinitial state, and hardly vary unless in an accident of the vehicle orthe like. However, if an offset in fact occurs between these, anadjustment is possible by the following means.

The camera is attached in such a manner that portions 513 and 514(characteristic points) that are characteristic of the driver's vehiclefit within its field of view, for example. The positions at which thesecharacteristic points are actually imaged by the camera are comparedagainst the information of the positions to be assumed by thesecharacteristic points when the camera is attached accurately in place,and an offset amount(s) is detected therebetween. Based on this detectedoffset amount(s), the position of any image that is taken thereafter maybe corrected, whereby an offset of the physical position of attachmentof the camera can be corrected for. If this correction sufficientlyembodies the performance that is required of the vehicle, then theadjustment per the above (2) may not be needed. By regularly performingthis adjustment during startup or operation of the vehicle 500, even ifan offset of the camera or the like occurs anew, it is possible tocorrect for the offset amount, thus helping safe travel.

However, this means is generally considered to result in poorer accuracyof adjustment than with the above means (2). When making an adjustmentbased on an image which is obtained by imaging a benchmark with thecamera, the azimuth of the benchmark can be determined with a highprecision, whereby a high accuracy of adjustment can be easily achieved.However, since this means utilizes a part of the vehicle body for theadjustment instead of a benchmark, it is rather difficult to enhance theaccuracy of azimuth determination. Thus, the resultant accuracy ofadjustment will be somewhat inferior. However, it may still be effectiveas a means of correction when the position of attachment of the cameraor the like is considerably altered for reasons such as an accident or alarge external force being applied to the camera or the like within thevehicle room, etc.

[Mapping of Target as Detected by Millimeter Wave Radar and Camera orthe Like: Matching Process]

In a fusion process, for a given target, it needs to be established thatan image thereof which is acquired with a camera or the like and radarinformation which is acquired with the millimeter wave radar pertain to“the same target”. For example, suppose that two obstacles (first andsecond obstacles), e.g., two bicycles, have appeared ahead of thevehicle 500. These two obstacles will be captured as camera images, anddetected as radar information of the millimeter wave radar. At thistime, the camera image and the radar information with respect to thefirst obstacle need to be mapped to each other so that they are bothdirected to the same target. Similarly, the camera image and the radarinformation with respect to the second obstacle need to be mapped toeach other so that they are both directed to the same target. If thecamera image of the first obstacle and the radar information of thesecond obstacle are mistakenly recognized to pertain to an identicalobject, a considerable accident may occur. Hereinafter, in the presentspecification, such a process of determining whether a target in thecamera image and a target in the radar image pertain to the same targetmay be referred to as a “matching process”.

This matching process may be implemented by various detection devices(or methods) described below. Hereinafter, these will be specificallydescribed. Note that the each of the following detection devices is tobe installed in the vehicle, and at least includes a millimeter waveradar detection section, an image detection section (e.g., a camera)which is oriented in a direction overlapping the direction of detectionby the millimeter wave radar detection section, and a matching section.Herein, the millimeter wave radar detection section includes a slotarray antenna according to any of the embodiments of the presentdisclosure, and at least acquires radar information in its own field ofview. The image acquisition section at least acquires image informationin its own field of view. The matching section includes a processingcircuit which matches a result of detection by the millimeter wave radardetection section against a result of detection by the image detectionsection to determine whether or not the same target is being detected bythe two detection sections. Herein, the image detection section may becomposed of a selected one of, or selected two or more of, an opticalcamera, LIDAR, an infrared radar, and an ultrasonic radar. The followingdetection devices differ from one another in terms of the detectionprocess at their respective matching section.

In a first detection device, the matching section performs two matchesas follows. A first match involves, for a target of interest that hasbeen detected by the millimeter wave radar detection section, obtainingdistance information and lateral position information thereof, and alsofinding a target that is the closest to the target of interest among atarget or two or more targets detected by the image detection section,and detecting a combination(s) thereof. A second match involves, for atarget of interest that has been detected by the image detectionsection, obtaining distance information and lateral position informationthereof, and also finding a target that is the closest to the target ofinterest among a target or two or more targets detected by themillimeter wave radar detection section, and detecting a combination(s)thereof. Furthermore, this matching section determines whether there isany matching combination between the combination(s) of such targets asdetected by the millimeter wave radar detection section and thecombination(s) of such targets as detected by the image detectionsection. Then, if there is any matching combination, it is determinedthat the same object is being detected by the two detection sections. Inthis manner, a match is attained between the respective targets thathave been detected by the millimeter wave radar detection section andthe image detection section.

A related technique is described in the specification of U.S. Pat. No.7,358,889, the entire disclosure of which is incorporated herein byreference. In this publication, the image detection section isillustrated by way of a so-called stereo camera that includes twocameras. However, this technique is not limited thereto. In the casewhere the image detection section includes a single camera, detectedtargets may be subjected to an image recognition process or the like asappropriate, in order to obtain distance information and lateralposition information of the targets. Similarly, a laser sensor such as alaser scanner may be used as the image detection section.

In a second detection device, the matching section matches a result ofdetection by the millimeter wave radar detection section and a result ofdetection by the image detection section every predetermined period oftime. If the matching section determines that the same target was beingdetected by the two detection sections in the previous result ofmatching, it performs a match by using this previous result of matching.Specifically, the matching section matches a target which is currentlydetected by the millimeter wave radar detection section and a targetwhich is currently detected by the image detection section, against thetarget which was determined in the previous result of matching to bebeing detected by the two detection sections. Then, based on the resultof matching for the target which is currently detected by the millimeterwave radar detection section and the result of matching for the targetwhich is currently detected by the image detection section, the matchingsection determines whether or not the same target is being detected bythe two detection sections. Thus, rather than directly matching theresults of detection by the two detection sections, this detectiondevice performs a chronological match between the two results ofdetection and a previous result of matching. Therefore, the accuracy ofdetection is improved over the case of only performing a momentarymatch, whereby stable matching is realized. In particular, even if theaccuracy of the detection section drops momentarily, matching is stillpossible because of utilizing past results of matching. Moreover, byutilizing the previous result of matching, this detection device is ableto easily perform a match between the two detection sections.

In the current match which utilizes the previous result of matching, ifthe matching section of this detection device determines that the sameobject is being detected by the two detection sections, then thematching section of this detection device excludes this determinedobject in performing matching between objects which are currentlydetected by the millimeter wave radar detection section and objectswhich are currently detected by the image detection section. Then, thismatching section determines whether there exists any identical objectthat is currently detected by the two detection sections. Thus, whiletaking into account the result of chronological matching, the detectiondevice also makes a momentary match based on two results of detectionthat are obtained from moment to moment. As a result, the detectiondevice is able to surely perform a match for any object that is detectedduring the current detection.

A related technique is described in the specification of U.S. Pat. No.7,417,580, the entire disclosure of which is incorporated herein byreference. In this publication, the image detection section isillustrated by way of a so-called stereo camera that includes twocameras. However, this technique is not limited thereto. In the casewhere the image detection section includes a single camera, detectedtargets may be subjected to an image recognition process or the like asappropriate, in order to obtain distance information and lateralposition information of the targets. Similarly, a laser sensor such as alaser scanner may be used as the image detection section.

In a third detection device, the two detection sections and matchingsection perform detection of targets and performs matches therebetweenat predetermined time intervals, and the results of such detection andthe results of such matching are chronologically stored to a storagemedium, e.g., memory. Then, based on a rate of change in the size of atarget in the image as detected by the image detection section, and on adistance to a target from the driver's vehicle and its rate of change(relative velocity with respect to the driver's vehicle) as detected bythe millimeter wave radar detection section, the matching sectiondetermines whether the target which has been detected by the imagedetection section and the target which has been detected by themillimeter wave radar detection section are an identical object.

When determining that these targets are an identical object, based onthe position of the target in the image as detected by the imagedetection section, and on the distance to the target from the driver'svehicle and/or its rate of change as detected by the millimeter waveradar detection section, the matching section predicts a possibility ofcollision with the vehicle.

A related technique is described in the specification of U.S. Pat. No.6,903,677, the entire disclosure of which is incorporated herein byreference.

As described above, in a fusion process of a millimeter wave radar andan imaging device such as a camera, an image which is obtained with thecamera or the like and radar information which is obtained with themillimeter wave radar are matched against each other. A millimeter waveradar incorporating the aforementioned array antenna according to anembodiment of the present disclosure can be constructed so as to have asmall size and high performance. Therefore, high performance anddownsizing, etc., can be achieved for the entire fusion processincluding the aforementioned matching process. This improves theaccuracy of target recognition, and enables safer travel control for thevehicle.

[Other Fusion Pocesses]

In a fusion process, various functions are realized based on a matchingprocess between an image which is obtained with a camera or the like andradar information which is obtained with the millimeter wave radardetection section. Examples of processing apparatuses that realizerepresentative functions of a fusion process will be described below.

Each of the following processing apparatuses is to be installed in avehicle, and at least includes: a millimeter wave radar detectionsection to transmit or receive electromagnetic waves in a predetermineddirection; an image acquisition section, such as a monocular camera,that has a field of view overlapping the field of view of the millimeterwave radar detection section; and a processing section which obtainsinformation therefrom to perform target detection and the like. Themillimeter wave radar detection section acquires radar information inits own field of view. The image acquisition section acquires imageinformation in its own field of view. A selected one, or selected two ormore of, an optical camera, LIDAR, an infrared radar, and an ultrasonicradar may be used as the image acquisition section. The processingsection can be implemented by a processing circuit which is connected tothe millimeter wave radar detection section and the image acquisitionsection. The following processing apparatuses differ from one anotherwith respect to the content of processing by this processing section.

In a first processing apparatus, the processing section extracts, froman image which is captured by the image acquisition section, a targetwhich is recognized to be the same as the target which is detected bythe millimeter wave radar detection section. In other words, a matchingprocess according to the aforementioned detection device is performed.Then, it acquires information of a right edge and a left edge of theextracted target image, and derives locus approximation lines, which arestraight lines or predetermined curved lines for approximating loci ofthe acquired right edge and the left edge, are derived for both edges.The edge which has a larger number of edges existing on the locusapproximation line is selected as a true edge of the target. The lateralposition of the target is derived on the basis of the position of theedge that has been selected as a true edge. This permits a furtherimprovement on the accuracy of detection of a lateral position of thetarget.

A related technique is described in the specification of U.S. Pat. No.8,610,620, the entire disclosure of which is incorporated herein byreference.

In a second processing apparatus, in determining the presence of atarget, the processing section alters a determination threshold to beused in checking for a target presence in radar information, on thebasis of image information. Thus, if a target image that may be anobstacle to vehicle travel has been confirmed with a camera or the like,or if the presence of a target has been estimated, etc., for example,the determination threshold for the target detection by the millimeterwave radar detection section can be optimized so that more accuratetarget information can be obtained. In other words, if the possibilityof the presence of an obstacle is high, the determination threshold isaltered so that this processing apparatus will surely be activated. Onthe other hand, if the possibility of the presence of an obstacle islow, the determination threshold is altered so that unwanted activationof this processing apparatus is prevented. This permits appropriateactivation of the system.

Furthermore in this case, based on radar information, the processingsection may designate a region of detection for the image information,and estimate a possibility of the presence of an obstacle on the basisof image information within this region. This makes for a more efficientdetection process.

A related technique is described in the specification of U.S. Pat. No.7,570,198, the entire disclosure of which is incorporated herein byreference.

In a third processing apparatus, the processing section performscombined displaying where images obtained from a plurality of differentimaging devices and a millimeter wave radar detection section and animage signal based on radar information are displayed on at least onedisplay device. In this displaying process, horizontal and verticalsynchronizing signals are synchronized between the plurality of imagingdevices and the millimeter wave radar detection section, and among theimage signals from these devices, selective switching to a desired imagesignal is possible within one horizontal scanning period or one verticalscanning period. This allows, on the basis of the horizontal andvertical synchronizing signals, images of a plurality of selected imagesignals to be displayed side by side; and, from the display device, acontrol signal for setting a control operation in the desired imagingdevice and the millimeter wave radar detection section is sent.

When a plurality of different display devices display respective imagesor the like, it is difficult to compare the respective images againstone another. Moreover, when display devices are provided separately fromthe third processing apparatus itself, there is poor operability for thedevice. The third processing apparatus would overcome such shortcomings.

A related technique is described in the specification of U.S. Pat. No.6,628,299 and the specification of U.S. Pat. No. 7,161,561, the entiredisclosure of each of which is incorporated herein by reference.

In a fourth processing apparatus, with respect to a target which isahead of a vehicle, the processing section instructs an imageacquisition section and a millimeter wave radar detection section toacquire an image and radar information containing that target. Fromwithin such image information, the processing section determines aregion in which the target is contained. Furthermore, the processingsection extracts radar information within this region, and detects adistance from the vehicle to the target and a relative velocity betweenthe vehicle and the target. Based on such information, the processingsection determines a possibility that the target will collide againstthe vehicle. This enables an early detection of a possible collisionwith a target.

A related technique is described in the specification of U.S. Pat. No.8,068,134, the entire disclosure of which is incorporated herein byreference.

In a fifth processing apparatus, based on radar information or through afusion process which is based on radar information and imageinformation, the processing section recognizes a target or two or moretargets ahead of the vehicle. The “target” encompasses any moving entitysuch as other vehicles or pedestrians, traveling lanes indicated bywhite lines on the road, road shoulders and any still objects (includinggutters, obstacles, etc.), traffic lights, pedestrian crossings, and thelike that may be there. The processing section may encompass a GPS(Global Positioning System) antenna. By using a GPS antenna, theposition of the driver's vehicle may be detected, and based on thisposition, a storage device (referred to as a map information databasedevice) that stores road map information may be searched in order toascertain a current position on the map. This current position on themap may be compared against a target or two or more targets that havebeen recognized based on radar information or the like, whereby thetraveling environment may be recognized. On this basis, the processingsection may extract any target that is estimated to hinder vehicletravel, find safer traveling information, and display it on a displaydevice, as necessary, to inform the driver.

A related technique is described in the specification of U.S. Pat. No.6,191,704, the entire disclosure of which is incorporated herein byreference.

The fifth processing apparatus may further include a data communicationdevice (having communication circuitry) that communicates with a mapinformation database device which is external to the vehicle. The datacommunication device may access the map information database device,with a period of e.g. once a week or once a month, to download thelatest map information therefrom. This allows the aforementionedprocessing to be performed with the latest map information.

Furthermore, the fifth processing apparatus may compare between thelatest map information that was acquired during the aforementionedvehicle travel and information that is recognized of a target or two ormore targets based on radar information, etc., in order to extracttarget information (hereinafter referred to as “map update information”)that is not included in the map information. Then, this map updateinformation may be transmitted to the map information database devicevia the data communication device. The map information database devicemay store this map update information in association with the mapinformation that is within the database, and update the current mapinformation itself, if necessary. In performing the update, respectivepieces of map update information that are obtained from a plurality ofvehicles may be compared against one another to check certainty of theupdate.

Note that this map update information may contain more detailedinformation than the map information which is carried by any currentlyavailable map information database device. For example, schematic shapesof roads may be known from commonly-available map information, but ittypically does not contain information such as the width of the roadshoulder, the width of the gutter that may be there, any newly occurringbumps or dents, shapes of buildings, and so on. Neither does it containheights of the roadway and the sidewalk, how a slope may connect to thesidewalk, etc . . . . Based on conditions which are separately set, themap information database device may store such detailed information(hereinafter referred to as “map update details information”) inassociation with the map information. Such map update detailsinformation provides a vehicle (including the driver's vehicle) withinformation which is more detailed than the original map information,thereby rending itself available for not only the purpose of ensuringsafe vehicle travel but also some other purposes. As used herein, a“vehicle (including the driver's vehicle)” may be e.g. an automobile, amotorcycle, a bicycle, or any autonomous vehicle to become available inthe future, e.g., an electric wheelchair. The map update detailsinformation is to be used when any such vehicle may travel.

(Recognition via Neural Network)

Each of the first to fifth processing apparatuses may further include asophisticated apparatus of recognition. The sophisticated apparatus ofrecognition may be provided external to the vehicle. In that case, thevehicle may include a high-speed data communication device thatcommunicates with the sophisticated apparatus of recognition. Thesophisticated apparatus of recognition may be constructed from a neuralnetwork, which may encompass so-called deep learning and the like. Thisneural network may include a convolutional neural network (hereinafterreferred to as “CNN”), for example. A CNN, a neural network that hasproven successful in image recognition, is characterized by possessingone or more sets of two layers, namely, a convolutional layer and apooling layer.

There exists at least three kinds of information as follows, any ofwhich may be input to a convolutional layer in the processing apparatus:

-   (1) information that is based on radar information which is acquired    by the millimeter wave radar detection section;-   (2) information that is based on specific image information which is    acquired, based on radar information, by the image acquisition    section; or-   (3) fusion information that is based on radar information and image    information which is acquired by the image acquisition section, or    information that is obtained based on such fusion information.

Based on information of any of the above kinds, or information based ona combination thereof, product-sum operations corresponding to aconvolutional layer are performed. The results are input to thesubsequent pooling layer, where data is selected according to apredetermined rule. In the case of max pooling where a maximum valueamong pixel values is chosen, for example, the rule may dictate that amaximum value be chosen for each split region in the convolutionallayer, this maximum value being regarded as the value of thecorresponding position in the pooling layer.

A sophisticated apparatus of recognition that is composed of a CNN mayinclude a single set of a convolutional layer and a pooling layer, or aplurality of such sets which are cascaded in series. This enablesaccurate recognition of a target, which is contained in the radarinformation and the image information, that may be around a vehicle.

Related techniques are described in the U.S. Pat. No. 8,861,842, thespecification of U.S. Pat. No. 9,286,524, and the specification of USPatent Application Publication No. 2016/0140424, the entire disclosureof each of which is incorporated herein by reference.

In a sixth processing apparatus, the processing section performsprocessing that is related to headlamp control of a vehicle. When avehicle travels in nighttime, the driver may check whether anothervehicle or a pedestrian exists ahead of the driver's vehicle, andcontrol a beam(s) from the headlamp(s) of the driver's vehicle toprevent the driver of the other vehicle or the pedestrian from beingdazzled by the headlamp(s) of the driver's vehicle. This sixthprocessing apparatus automatically controls the headlamp(s) of thedriver's vehicle by using radar information, or a combination of radarinformation and an image taken by a camera or the like.

Based on radar information, or through a fusion process based on radarinformation and image information, the processing section detects atarget that corresponds to a vehicle or pedestrian ahead of the vehicle.In this case, a vehicle ahead of a vehicle may encompass a precedingvehicle that is ahead, a vehicle or a motorcycle in the oncoming lane,and so on. When detecting any such target, the processing section issuesa command to lower the beam(s) of the headlamp(s). Upon receiving thiscommand, the control section (control circuit) which is internal to thevehicle may control the headlamp(s) to lower the beam(s) therefrom.

Related techniques are described in the specification of U.S. Pat. No.6,403,942, the specification of U.S. Pat. No. 6,611,610, thespecification of U.S. Pat. No. 8,543,277, the specification of U.S. Pat.No. 8,593,521, and the specification of U.S. Pat. No. 8,636,393, theentire disclosure of each of which is incorporated herein by reference.

According to the above-described processing by the millimeter wave radardetection section, and the above-described fusion process by themillimeter wave radar detection section and an imaging device such as acamera, the millimeter wave radar can be constructed so as to have asmall size and high performance, whereby high performance anddownsizing, etc., can be achieved for the radar processing or the entirefusion process. This improves the accuracy of target recognition, andenables safer travel control for the vehicle.

APPLICATION EXAMPLE 2 Various Monitoring Systems (Natural Elements,Buildings, Roads, Watch, Security)

A millimeter wave radar (radar system) incorporating an array antennaaccording to an embodiment of the present disclosure also has a widerange of applications in the fields of monitoring, which may encompassnatural elements, weather, buildings, security, nursing care, and thelike. In a monitoring system in this context, a monitoring apparatusthat includes the millimeter wave radar may be installed e.g. at a fixedposition, in order to perpetually monitor a subject(s) of monitoring.Regarding the given subject(s) of monitoring, the millimeter wave radarhas its resolution of detection adjusted and set to an optimum value.

A millimeter wave radar incorporating an array antenna according to anembodiment of the present disclosure is capable of detection with aradio frequency electromagnetic wave exceeding e.g. 100 GHz. As for themodulation band in those schemes which are used in radar recognition,e.g., the FMCW method, the millimeter wave radar currently achieves awide band exceeding 4 GHz, which supports the aforementioned Ultra WideBand (UWB). Note that the modulation band is related to the rangeresolution. In a conventional patch antenna, the modulation band was upto about 600 MHz, thus resulting in a range resolution of 25 cm. On theother hand, a millimeter wave radar associated with the present arrayantenna has a range resolution of 3.75 cm, indicative of a performancewhich rivals the range resolution of conventional LIDAR. Whereas anoptical sensor such as LIDAR is unable to detect a target in nighttimeor bad weather as mentioned above, a millimeter wave radar is alwayscapable of detection, regardless of daytime or nighttime andirrespective of weather. As a result, a millimeter wave radar associatedwith the present array antenna is available for a variety ofapplications which were not possible with a millimeter wave radarincorporating any conventional patch antenna.

FIG. 33 is a diagram showing an exemplary construction for a monitoringsystem 1500 based on millimeter wave radar. The monitoring system 1500based on millimeter wave radar at least includes a sensor section 1010and a main section 1100. The sensor section 1010 at least includes anantenna 1011 which is aimed at the subject of monitoring 1015, amillimeter wave radar detection section 1012 which detects a targetbased on a transmitted or received electromagnetic wave, and acommunication section (communication circuit) 1013 which transmitsdetected radar information. The main section 1100 at least includes acommunication section (communication circuit) 1103 which receives radarinformation, a processing section (processing circuit) 1101 whichperforms predetermined processing based on the received radarinformation, and a data storage section (storage medium) 1102 in whichpast radar information and other information that is needed for thepredetermined processing, etc., are stored. Telecommunication lines 1300exist between the sensor section 1010 and the main section 1100, viawhich transmission and reception of information and commands occurbetween them. As used herein, the telecommunication lines may encompassany of a general-purpose communications network such as the Internet, amobile communications network, dedicated telecommunication lines, and soon, for example. Note that the present monitoring system 1500 may bearranged so that the sensor section 1010 and the main section 1100 aredirectly connected, rather than via telecommunication lines. In additionto the millimeter wave radar, the sensor section 1010 may also includean optical sensor such as a camera. This will permit target recognitionthrough a fusion process which is based on radar information and imageinformation from the camera or the like, thus enabling a moresophisticated detection of the subject of monitoring 1015 or the like.

Hereinafter, examples of monitoring systems embodying these applicationswill be specifically described.

[Natural Element Monitoring System]

A first monitoring system is a system that monitors natural elements(hereinafter referred to as a “natural element monitoring system”). Withreference to FIG. 33, this natural element monitoring system will bedescribed. Subjects of monitoring 1015 of the natural element monitoringsystem 1500 may be, for example, a river, the sea surface, a mountain, avolcano, the ground surface, or the like. For example, when a river isthe subject of monitoring 1015, the sensor section 1010 being secured toa fixed position perpetually monitors the water surface of the river1015. This water surface information is perpetually transmitted to aprocessing section 1101 in the main section 1100. Then, if the watersurface reaches a certain height or above, the processing section 1101informs a distinct system 1200 which separately exists from themonitoring system (e.g., a weather observation monitoring system), viathe telecommunication lines 1300. Alternatively, the processing section1101 may send information to a system (not shown) which manages thewater gate, whereby the system if instructed to automatically close awater gate, etc. (not shown) which is provided at the river 1015.

The natural element monitoring system 1500 is able to monitor aplurality of sensor sections 1010, 1020, etc., with the single mainsection 1100. When the plurality of sensor sections are distributed overa certain area, the water levels of rivers in that area can be graspedsimultaneously. This allows to make an assessment as to how the rainfallin this area may affect the water levels of the rivers, possibly leadingto disasters such as floods. Information concerning this can be conveyedto the distinct system 1200 (e.g., a weather observation monitoringsystem) via the telecommunication lines 1300. Thus, the distinct system1200 (e.g., a weather observation monitoring system) is able to utilizethe conveyed information for weather observation or disaster predictionin a wider area.

The natural element monitoring system 1500 is also similarly applicableto any natural element other than a river. For example, the subject ofmonitoring of a monitoring system that monitors tsunamis or storm surgesis the sea surface level. It is also possible to automatically open orclose the water gate of a seawall in response to a rise in the seasurface level. Alternatively, the subject of monitoring of a monitoringsystem that monitors landslides to be caused by rainfall, earthquakes,or the like may be the ground surface of a mountainous area, etc.

[Traffic Monitoring System]

A second monitoring system is a system that monitors traffic(hereinafter referred to as a “traffic monitoring system”). The subjectof monitoring of this traffic monitoring system may be, for example, arailroad crossing, a specific railroad, an airport runway, a roadintersection, a specific road, a parking lot, etc.

For example, when the subject of monitoring is a railroad crossing, thesensor section 1010 is placed at a position where the inside of thecrossing can be monitored. In this case, in addition to the millimeterwave radar, the sensor section 1010 may also include an optical sensorsuch as a camera, which will allow a target (subject of monitoring) tobe detected from more perspectives, through a fusion process based onradar information and image information. The target information which isobtained with the sensor section 1010 is sent to the main section 1100via the telecommunication lines 1300. The main section 1100 collectsother information (e.g., train schedule information) that may be neededin a more sophisticated recognition process or control, and issuesnecessary control instructions or the like based thereon. As usedherein, a necessary control instruction may be, for example, aninstruction to stop a train when a person, a vehicle, etc. is foundinside the crossing when it is closed.

If the subject of monitoring is a runway at an airport, for example, aplurality of sensor sections 1010, 1020, etc., may be placed along therunway so as to set the runway to a predetermined resolution, e.g., aresolution that allows any foreign object on the runway that is 5 cm by5 cm or larger to be detected. The monitoring system 1500 perpetuallymonitors the runway, regardless of daytime or nighttime and irrespectiveof weather. This function is enabled by the very ability of themillimeter wave radar according to an embodiment of the presentdisclosure to support UWB. Moreover, since the present millimeter waveradar device can be embodied with a small size, a high resolution, and alow cost, it provides a realistic solution for covering the entirerunway surface from end to end. In this case, the main section 1100keeps the plurality of sensor sections 1010, 1020, etc., underintegrated management. If a foreign object is found on the runway, themain section 1100 transmits information concerning the position and sizeof the foreign object to an air-traffic control system (not shown). Uponreceiving this, the air-traffic control system temporarily prohibitstakeoff and landing on that runway. In the meantime, the main section1100 transmits information concerning the position and size of theforeign object to a separately-provided vehicle, which automaticallycleans the runway surface, etc., for example. Upon receive this, thecleaning vehicle may autonomously move to the position where the foreignobject exists, and automatically remove the foreign object. Once removalof the foreign object is completed, the cleaning vehicle transmitsinformation of the completion to the main section 1100. Then, the mainsection 1100 again confirms that the sensor section 1010 or the likewhich has detected the foreign object now reports that “no foreignobject exists” and that it is safe now, and informs the air-trafficcontrol system of this. Upon receiving this, the air-traffic controlsystem may lift the prohibition of takeoff and landing from the runway.

Furthermore, in the case where the subject of monitoring is a parkinglot, for example, it may be possible to automatically recognize whichposition in the parking lot is currently vacant. A related technique isdescribed in the specification of U.S. Pat. No. 6,943,726, the entiredisclosure of which is incorporated herein by reference.

[Security Monitoring System]

A third monitoring system is a system that monitors a trespasser into apiece of private land or a house (hereinafter referred to as a “securitymonitoring system”). The subject of monitoring of this securitymonitoring system may be, for example, a specific region within a pieceof private land or a house, etc.

For example, if the subject of monitoring is a piece of private land,the sensor section(s) 1010 may be placed at one position, or two or morepositions where the sensor section(s) 1010 is able to monitor it. Inthis case, in addition to the millimeter wave radar, the sensorsection(s) 1010 may also include an optical sensor such as a camera,which will allow a target (subject of monitoring) to be detected frommore perspectives, through a fusion process based on radar informationand image information. The target information which was obtained by thesensor section 1010(s) is sent to the main section 1100 via thetelecommunication lines 1300. The main section 1100 collects otherinformation (e.g., reference data or the like needed to accuratelyrecognize whether the trespasser is a person or an animal such as a dogor a bird) that may be needed in a more sophisticated recognitionprocess or control, and issues necessary control instructions or thelike based thereon. As used herein, a necessary control instruction maybe, for example, an instruction to sound an alarm or activate lightingthat is installed in the premises, and also an instruction to directlyreport to a person in charge of the premises via mobiletelecommunication lines or the like, etc. The processing section 1101 inthe main section 1100 may allow an internalized, sophisticated apparatusof recognition (that adopts deep learning or a like technique) torecognize the detected target. Alternatively, such a sophisticatedapparatus of recognition may be provided externally, in which case thesophisticated apparatus of recognition may be connected via thetelecommunication lines 1300.

A related technique is described in the specification of U.S. Pat. No.7,425,983, the entire disclosure of which is incorporated herein byreference.

Another embodiment of such a security monitoring system may be a humanmonitoring system to be installed at a boarding gate at an airport, astation wicket, an entrance of a building, or the like. The subject ofmonitoring of such a human monitoring system may be, for example, aboarding gate at an airport, a station wicket, an entrance of abuilding, or the like.

If the subject of monitoring is a boarding gate at an airport, thesensor section(s) 1010 may be installed in a machine for checkingpersonal belongings at the boarding gate, for example. In this case,there may be two checking methods as follows. In a first method, themillimeter wave radar transmits an electromagnetic wave, and receivesthe electromagnetic wave as it reflects off a passenger (which is thesubject of monitoring), thereby checking personal belongings or the likeof the passenger. In a second method, a weak millimeter wave which isradiated from the passenger's own body is received by the antenna, thuschecking for any foreign object that the passenger may be hiding. In thelatter method, the millimeter wave radar preferably has a function ofscanning the received millimeter wave. This scanning function may beimplemented by using digital beam forming, or through a mechanicalscanning operation. Note that the processing by the main section 1100may utilize a communication process and a recognition process similar tothose in the above-described examples.

[Building Inspection System (Non-Destructive Inspection)]

A fourth monitoring system is a system that monitors or checks theconcrete material of a road, a railroad overpass, a building, etc., orthe interior of a road or the ground, etc., (hereinafter referred to asa “building inspection system”). The subject of monitoring of thisbuilding inspection system may be, for example, the interior of theconcrete material of an overpass or a building, etc., or the interior ofa road or the ground, etc.

For example, if the subject of monitoring is the interior of a concretebuilding, the sensor section 1010 is structured so that the antenna 1011can make scan motions along the surface of a concrete building. As usedherein, “scan motions” may be implemented manually, or a stationary railfor the scan motion may be separately provided, upon which to cause themovement by using driving power from an electric motor or the like. Inthe case where the subject of monitoring is a road or the ground, theantenna 1011 may be installed face-down on a vehicle or the like, andthe vehicle may be allowed to travel at a constant velocity, thuscreating a “scan motion”. The electromagnetic wave to be used by thesensor section 1010 may be a millimeter wave in e.g. the so-calledterahertz region, exceeding 100 GHz. As described earlier, even with anelectromagnetic wave over e.g. 100 GHz, an array antenna according to anembodiment of the present disclosure can be adapted to have smallerlosses than do conventional patch antennas or the like. Anelectromagnetic wave of a higher frequency is able to permeate deeperinto the subject of checking, such as concrete, thereby realizing a moreaccurate non-destructive inspection. Note that the processing by themain section 1100 may also utilize a communication process and arecognition process similar to those in the other monitoring systemsdescribed above.

A related technique is described in the specification of U.S. Pat. No.6,661,367, the entire disclosure of which is incorporated herein byreference.

[Human Monitoring System]

A fifth monitoring system is a system that watches over a person who issubject to nursing care (hereinafter referred to as a “human watchsystem”). The subject of monitoring of this human watch system may be,for example, a person under nursing care or a patient in a hospital,etc.

For example, if the subject of monitoring is a person under nursing carewithin a room of a nursing care facility, the sensor section(s) 1010 isplaced at one position, or two or more positions inside the room wherethe sensor section(s) 1010 is able to monitor the entirety of the insideof the room. In this case, in addition to the millimeter wave radar, thesensor section 1010 may also include an optical sensor such as a camera.In this case, the subject of monitoring can be monitored from moreperspectives, through a fusion process based on radar information andimage information. On the other hand, when the subject of monitoring isa person, from the standpoint of privacy protection, monitoring with acamera or the like may not be appropriate. Therefore, sensor selectionsmust be made while taking this aspect into consideration. Note thattarget detection by the millimeter wave radar will allow a person, whois the subject of monitoring, to be captured not by his or her image,but by a signal (which is, as it were, a shadow of the person).Therefore, the millimeter wave radar may be considered as a desirablesensor from the standpoint of privacy protection.

Information of the person under nursing care which has been obtained bythe sensor section(s) 1010 is sent to the main section 1100 via thetelecommunication lines 1300. The main section 1100 collects otherinformation (e.g., reference data or the like needed to accuratelyrecognize target information of the person under nursing care) that maybe needed in a more sophisticated recognition process or control, andissues necessary control instructions or the like based thereon. As usedherein, a necessary control instruction may be, for example, aninstruction to directly report a person in charge based on the result ofdetection, etc. The processing section 1101 in the main section 1100 mayallow an internalized, sophisticated apparatus of recognition (thatadopts deep learning or a like technique) to recognize the detectedtarget. Alternatively, such a sophisticated apparatus of recognition maybe provided externally, in which case the sophisticated apparatus ofrecognition may be connected via the telecommunication lines 1300.

In the case where a person is the subject of monitoring of themillimeter wave radar, at least the two following functions may beadded.

A first function is a function of monitoring the heart rate and/or therespiratory rate. In the case of a millimeter wave radar, anelectromagnetic wave is able to see through the clothes to detect theposition and motions of the skin surface of a person's body. First, theprocessing section 1101 detects a person who is the subject ofmonitoring and an outer shape thereof. Next, in the case of detecting aheart rate, for example, a position on the body surface where theheartbeat motions are easy to detect may be identified, and the motionsthere may be chronologically detected. This allows a heart rate perminute to be detected, for example. The same is also true when detectinga respiratory rate. By using this function, the health status of aperson under nursing care can be perpetually checked, thus enabling ahigher-quality watch over a person under nursing care.

A second function is a function of fall detection. A person undernursing care such as an elderly person may fall from time to time, dueto weakened legs and feet. When a person falls, the velocity oracceleration of a specific site of the person's body, e.g., the head,will reach a certain level or greater. When the subject of monitoring ofthe millimeter wave radar is a person, the relative velocity oracceleration of the target of interest can be perpetually detected.Therefore, by identifying the head as the subject of monitoring, forexample, and chronologically detecting its relative velocity oracceleration, a fall can be recognized when a velocity of a certainvalue or greater is detected. When recognizing a fall, the processingsection 1101 can issue an instruction or the like corresponding topertinent nursing care assistance, for example.

Note that the sensor section(s) 1010 is secured to a fixed position(s)in the above-described monitoring system or the like. However, thesensor section(s) 1010 can also be installed on a moving entity, e.g., arobot, a vehicle, a flying object such as a drone. As used herein, thevehicle or the like may encompass not only an automobile, but also asmaller sized moving entity such as an electric wheelchair, for example.In this case, this moving entity may include an internal GPS unit whichallows its own current position to be always confirmed. In addition,this moving entity may also have a function of further improving theaccuracy of its own current position by using map information and themap update information which has been described with respect to theaforementioned fifth processing apparatus.

Furthermore, in any device or system that is similar to theabove-described first to third detection devices, first to sixthprocessing apparatuses, first to fifth monitoring systems, etc., a likeconstruction may be adopted to utilize an array antenna or a millimeterwave radar according to an embodiment of the present disclosure.

APPLICATION EXAMPLE 3 Communication System First Example ofCommunication System

The waveguide device and antenna device (array antenna) according to thepresent disclosure can be used for the transmitter and/or receiver withwhich a communication system (telecommunication system) is constructed.The waveguide device and antenna device according to the presentdisclosure are composed of layered conductive members, and therefore areable to keep the transmitter and/or receiver size smaller than in thecase of using a hollow waveguide. Moreover, there is no need fordielectric, and thus the dielectric loss of electromagnetic waves can bekept smaller than in the case of using a microstrip line. Therefore, acommunication system including a small and highly efficient transmitterand/or receiver can be constructed.

Such a communication system may be an analog type communication systemwhich transmits or receives an analog signal that is directly modulated.However, a digital communication system may be adopted in order toconstruct a more flexible and higher-performance communication system.

Hereinafter, with reference to FIG. 34, a digital communication system800A in which a waveguide device and an antenna device according to anembodiment of the present disclosure are used will be described.

FIG. 34 is a block diagram showing a construction for the digitalcommunication system 800A. The communication system 800A includes atransmitter 810A and a receiver 820A. The transmitter 810A includes ananalog to digital (A/D) converter 812, an encoder 813, a modulator 814,and a transmission antenna 815. The receiver 820A includes a receptionantenna 825, a demodulator 824, a decoder 823, and a digital to analog(D/A) converter 822. The at least one of the transmission antenna 815and the reception antenna 825 may be implemented by using an arrayantenna according to an embodiment of the present disclosure. In thisexemplary application, the circuitry including the modulator 814, theencoder 813, the A/D converter 812, and so on, which are connected tothe transmission antenna 815, is referred to as the transmissioncircuit. The circuitry including the demodulator 824, the decoder 823,the D/A converter 822, and so on, which are connected to the receptionantenna 825, is referred to as the reception circuit. The transmissioncircuit and the reception circuit may be collectively referred to as thecommunication circuit.

With the analog to digital (A/D) converter 812, the transmitter 810Aconverts an analog signal which is received from the signal source 811to a digital signal. Next, the digital signal is encoded by the encoder813. As used herein, “encoding” means altering the digital signal to betransmitted into a format which is suitable for communication. Examplesof such encoding include CDM (Code-Division Multiplexing) and the like.Moreover, any conversion for effecting TDM (Time-Division Multiplexing)or FDM (Frequency Division Multiplexing), or OFDM (Orthogonal FrequencyDivision Multiplexing) is also an example of encoding. The encodedsignal is converted by the modulator 814 into a radio frequency signal,so as to be transmitted from the transmission antenna 815.

In the field of communications, a wave representing a signal to besuperposed on a carrier wave may be referred to as a “signal wave”;however, the term “signal wave” as used in the present specificationdoes not carry that definition. A “signal wave” as referred to in thepresent specification is broadly meant to be any electromagnetic wave topropagate in a waveguide, or any electromagnetic wave fortransmission/reception via an antenna element.

The receiver 820A restores the radio frequency signal that has beenreceived by the reception antenna 825 to a low-frequency signal at thedemodulator 824, and to a digital signal at the decoder 823. The decodeddigital signal is restored to an analog signal by the digital to analog(D/A) converter 822, and is sent to a data sink (data receiver) 821.Through the above processes, a sequence of transmission and receptionprocesses is completed.

When the communicating agent is a digital appliance such as a computer,analog to digital conversion of the transmission signal and digital toanalog conversion of the reception signal are not needed in theaforementioned processes. Thus, the analog to digital converter 812 andthe digital to analog converter 822 in FIG. 34 may be omitted. A systemof such construction is also encompassed within a digital communicationsystem.

In a digital communication system, in order to ensure signal intensityor expand channel capacity, various methods may be adopted. Many suchmethods are also effective in a communication system which utilizesradio waves of the millimeter wave band or the terahertz band.

Radio waves in the millimeter wave band or the terahertz band havehigher straightness than do radio waves of lower frequencies, andundergoes less diffraction, i.e., bending around into the shadow side ofan obstacle. Therefore, it is not uncommon for a receiver to fail todirectly receive a radio wave that has been transmitted from atransmitter. Even in such situations, reflected waves may often bereceived, but a reflected wave of a radio wave signal is often poorer inquality than is the direct wave, thus making stable reception moredifficult. Furthermore, a plurality of reflected waves may arrivethrough different paths. In that case, the reception waves withdifferent path lengths might differ in phase from one another, thuscausing multi-path fading.

As a technique for improving such situations, a so-called antennadiversity technique may be used. In this technique, at least one of thetransmitter and the receiver includes a plurality of antennas. If theplurality of antennas are parted by distances which differ from oneanother by at least about the wavelength, the resulting states of thereception waves will be different. Accordingly, the antenna that iscapable of transmission/reception with the highest quality among all isselectively used, thereby enhancing the reliability of communication.Alternatively, signals which are obtained from more than one antenna maybe merged for an improved signal quality.

In the communication system 800A shown in FIG. 34, for example, thereceiver 820A may include a plurality of reception antennas 825. In thiscase, a switcher exists between the plurality of reception antennas 825and the demodulator 824. Through the switcher, the receiver 820Aconnects the antenna that provides the highest-quality signal among theplurality of reception antennas 825 to the demodulator 824. In thiscase, the transmitter 810A may also include a plurality of transmissionantennas 815.

Second Example of Communication System

FIG. 35 is a block diagram showing an example of a communication system800B including a transmitter 810B which is capable of varying theradiation pattern of radio waves. In this exemplary application, thereceiver is identical to the receiver 820A shown in FIG. 34; for thisreason, the receiver is omitted from illustration in FIG. 35. Inaddition to the construction of the transmitter 810A, the transmitter810B also includes an antenna array 815 b, which includes a plurality ofantenna elements 8151. The antenna array 815 b may be an array antennaaccording to an embodiment of the present disclosure. The transmitter810B further includes a plurality of phase shifters (PS) 816 which arerespectively connected between the modulator 814 and the plurality ofantenna elements 8151. In the transmitter 810B, an output of themodulator 814 is sent to the plurality of phase shifters 816, wherephase differences are imparted and the resultant signals are led to theplurality of antenna elements 8151. In the case where the plurality ofantenna elements 8151 are disposed at equal intervals, if a radiofrequency signal whose phase differs by a certain amount with respect toan adjacent antenna element is fed to each antenna element 8151, a mainlobe 817 of the antenna array 815 b will be oriented in an azimuth whichis inclined from the front, this inclination being in accordance withthe phase difference. This method may be referred to as beam forming.

The azimuth of the main lobe 817 may be altered by allowing therespective phase shifters 816 to impart varying phase differences. Thismethod may be referred to as beam steering. By finding phase differencesthat are conducive to the best transmission/reception state, thereliability of communication can be enhanced. Although the example hereillustrates a case where the phase difference to be imparted by thephase shifters 816 is constant between any adjacent antenna elements8151, this is not limiting. Moreover, phase differences may be impartedso that the radio wave will be radiated in an azimuth which allows notonly the direct wave but also reflected waves to reach the receiver.

A method called null steering can also be used in the transmitter 810B.This is a method where phase differences are adjusted to create a statewhere the radio wave is radiated in no specific direction. By performingnull steering, it becomes possible to restrain radio waves from beingradiated toward any other receiver to which transmission of the radiowave is not intended. This can avoid interference. Although a very broadfrequency band is available to digital communication utilizingmillimeter waves or terahertz waves, it is nonetheless preferable tomake as efficient a use of the bandwidth as possible. By using nullsteering, plural instances of transmission/reception can be performedwithin the same band, whereby efficiency of utility of the bandwidth canbe enhanced. A method which enhances the efficiency of utility of thebandwidth by using techniques such as beam forming, beam steering, andnull steering may sometimes be referred to as SDMA (Spatial DivisionMultiple Access).

Third Example of Communication System

In order to increase the channel capacity in a specific frequency band,a method called MIMO (Multiple-Input and Multiple-Output) may beadopted. Under MIMO, a plurality of transmission antennas and aplurality of reception antennas are used. A radio wave is radiated fromeach of the plurality of transmission antennas. In one example,respectively different signals may be superposed on the radio waves tobe radiated. Each of the plurality of reception antennas receives all ofthe transmitted plurality of radio waves. However, since differentreception antennas will receive radio waves that arrive throughdifferent paths, differences will occur among the phases of the receivedradio waves. By utilizing these differences, it is possible to, at thereceiver side, separate the plurality of signals which were contained inthe plurality of radio waves.

The waveguide device and antenna device according to the presentdisclosure can also be used in a communication system which utilizesMIMO. Hereinafter, an example such a communication system will bedescribed.

FIG. 36 is a block diagram showing an example of a communication system800C implementing a MIMO function. In the communication system 800C, atransmitter 830 includes an encoder 832, a TX-MIMO processor 833, andtwo transmission antennas 8351 and 8352. A receiver 840 includes tworeception antennas 8451 and 8452, an RX-MIMO processor 843, and adecoder 842. Note that the number of transmission antennas and thenumber of reception antennas may each be greater than two. Herein, forease of explanation, an example where there are two antennas of eachkind will be illustrated. In general, the channel capacity of an MIMOcommunication system will increase in proportion to the number ofwhichever is the fewer between the transmission antennas and thereception antennas.

Having received a signal from the data signal source 831, thetransmitter 830 encodes the signal at the encoder 832 so that the signalis ready for transmission. The encoded signal is distributed by theTX-MIMO processor 833 between the two transmission antennas 8351 and8352.

In a processing method according to one example of the MIMO method, theTX-MIMO processor 833 splits a sequence of encoded signals into two,i.e., as many as there are transmission antennas 8352, and sends them inparallel to the transmission antennas 8351 and 8352. The transmissionantennas 8351 and 8352 respectively radiate radio waves containinginformation of the split signal sequences. When there are N transmissionantennas, the signal sequence is split into N. The radiated radio wavesare simultaneously received by the two reception antennas 8451 and 8452.In other words, in the radio waves which are received by each of thereception antennas 8451 and 8452, the two signals which were split atthe time of transmission are mixedly contained. Separation between thesemixed signals is achieved by the RX-MIMO processor 843.

The two mixed signals can be separated by paying attention to the phasedifferences between the radio waves, for example. A phase differencebetween two radio waves of the case where the radio waves which havearrived from the transmission antenna 8351 are received by the receptionantennas 8451 and 8452 is different from a phase difference between tworadio waves of the case where the radio waves which have arrived fromthe transmission antenna 8352 are received by the reception antennas8451 and 8452. That is, the phase difference between reception antennasdiffers depending on the path of transmission/reception. Moreover,unless the spatial relationship between a transmission antenna and areception antenna is changed, the phase difference therebetween remainsunchanged. Therefore, based on correlation between reception signalsreceived by the two reception antennas, as shifted by a phase differencewhich is determined by the path of transmission/reception, it ispossible to extract any signal that is received through that path oftransmission/reception. The RX-MIMO processor 843 may separate the twosignal sequences from the reception signal e.g. by this method, thusrestoring the signal sequence before the split. The restored signalsequence still remains encoded, and therefore is sent to the decoder 842so as to be restored to the original signal there. The restored signalis sent to the data sink 841.

Although the MIMO communication system 800C in this example transmits orreceives a digital signal, an MIMO communication system which transmitsor receives an analog signal can also be realized. In that case, inaddition to the construction of FIG. 36, an analog to digital converterand a digital to analog converter as have been described with referenceto FIG. 34 are provided. Note that the information to be used indistinguishing between signals from different transmission antennas isnot limited to phase difference information. Generally speaking, for adifferent combination of a transmission antenna and a reception antenna,the received radio wave may differ not only in terms of phase, but alsoin scatter, fading, and other conditions. These are collectivelyreferred to as CSI (Channel State Information). CSI may be utilized indistinguishing between different paths of transmission/reception in asystem utilizing MIMO.

Note that it is not an essential requirement that the plurality oftransmission antennas radiate transmission waves containing respectivelyindependent signals. So long as separation is possible at the receptionantenna side, each transmission antenna may radiate a radio wavecontaining a plurality of signals. Moreover, beam forming may beperformed at the transmission antenna side, while a transmission wavecontaining a single signal, as a synthetic wave of the radio waves fromthe respective transmission antennas, may be formed at the receptionantenna. In this case, too, each transmission antenna is adapted so asto radiate a radio wave containing a plurality of signals.

In this third example, too, as in the first and second examples, variousmethods such as CDM, FDM, TDM, and OFDM may be used as a method ofsignal encoding. In a communication system, a circuit board thatimplements an integrated circuit (referred to as a signal processingcircuit or a communication circuit) for processing signals may bestacked as a layer on the waveguide device and antenna device accordingto an embodiment of the present disclosure. Since the waveguide deviceand antenna device according to an embodiment of the present disclosureis structured so that plate-like conductive members are layered therein,it is easy to further stack a circuit board thereupon. By adopting suchan arrangement, a transmitter and a receiver which are smaller in volumethan in the case where a hollow waveguide or the like is employed can berealized.

In the first to third examples of the communication system as describedabove, each element of a transmitter or a receiver, e.g., an analog todigital converter, a digital to analog converter, an encoder, a decoder,a modulator, a demodulator, a TX-MIMO processor, or an RX-MIMOprocessor, is illustrated as one independent element in FIGS. 34, 35,and 36; however, these do not need to be discrete. For example, all ofthese elements may be realized by a single integrated circuit.Alternatively, some of these elements may be combined so as to berealized by a single integrated circuit. Either case qualifies as anembodiment of the present invention so long as the functions which havebeen described in the present disclosure are realized thereby. Asdescribed above, the present disclosure encompasses devices as recitedin the following Items.

[Item 1]

A slot antenna device, comprising:

a first electrically conductive member having a first electricallyconductive surface on a front side and a second electrically conductivesurface on a rear side, and having at least one slot extending from thefirst electrically conductive surface through to the second electricallyconductive surface;

a second electrically conductive member on the rear side of the firstelectrically conductive member, the second electrically conductivemember having a third electrically conductive surface on the front side,the third electrically conductive surface opposing the secondelectrically conductive surface;

a ridge-shaped waveguide member on the second electrically conductivesurface of the first electrically conductive member, the waveguidemember having an electrically-conductive waveguide face that opposes thethird electrically conductive surface and extending alongside the thirdelectrically conductive surface; and

an artificial magnetic conductor on at least one of the secondelectrically conductive surface and the third electrically conductivesurface, the artificial magnetic conductor extending on both sides ofthe waveguide member, wherein,

the third electrically conductive surface, the waveguide face, and theartificial magnetic conductor define a waveguide in a gap extendingbetween the third electrically conductive surface and the waveguideface;

the waveguide member includes a first ridge and a second ridge;

one end of the first ridge and one end of the second ridge are opposedto each other;

as viewed from a direction perpendicular to the waveguide face, the atleast one slot is located between the one end of the first ridge and theone end of the second ridge; and

the at least one slot is open to an external space through the firstelectrically conductive surface.

[Item 2]

The slot antenna device of item 1, wherein,

the first ridge and the second ridge have end faces that oppose eachother; and

the end faces of the first ridge and the second ridge are continuouswith an inner wall surface of the slot without being stepped.

[Item 3]

The slot antenna device of item 1 or 2, wherein the first electricallyconductive surface of the first electrically conductive member has ashape that defines at least one horn communicating with the at least oneslot.

[Item 4]

The slot antenna device of any of items 1 to 3, wherein,

the artificial magnetic conductor includes a plurality of electricallyconductive rods on the second electrically conductive surace; and

each of the plurality of electrically conductive rods have a leading endopposed to the third electrically conductive surface and a rootconnected to the second electrically conductive surface.

[Item 5]

The slot antenna device of any of items 1 to 4, wherein the at least oneslot have an H shape that includes a pair of vertical portions and alateral portion connecting between central portions of the pair ofvertical portions.

[Item 6]

The slot antenna device any of items 1 to 5, wherein,

the first electrically conductive member has a plurality of slotsincluding the at least one slot, the plurality of slots being arrangedalong a direction that the waveguide member extends;

the waveguide member includes a plurality of ridges including the firstridge and the second ridge; and

as viewed from a direction perpendicular to the waveguide face, each ofthe plurality of slots is located between the opposing ends of twoadjacent ones of the plurality of ridges; and

each of the plurality of slots is open to the external space through thefirst electrically conductive surface.

[Item 7]

The slot antenna device of any of items 1 to 6, wherein the secondelectrically conductive member further has: a fourth electricallyconductive surface on the rear side; and a port extending from the thirdelectrically conductive surface through to the fourth electricallyconductive surface and opposing the waveguide face of the waveguidemember.

[Item 8]

The slot antenna device of item 7, further comprising:

a third electrically conductive member having a fifth electricallyconductive surface on the front side, the fifth electrically conductivesurface opposing the fourth electrically conductive surface; and

a ridge-shaped second waveguide member on the fifth electricallyconductive surface, the second waveguide member having anelectrically-conductive waveguide face that opposes the fourthelectrically conductive surface and extending alongside the fourthelectrically conductive surface.

[Item 9]

The slot antenna device of item 7, further comprising:

a third electrically conductive member having a fifth electricallyconductive surface on the front side, the fifth electrically conductivesurface opposing the fourth electrically conductive surface; and

a ridge-shaped second waveguide member on the fourth electricallyconductive surface, the second waveguide member having anelectrically-conductive waveguide face that opposes the fifthelectrically conductive surface and extending alongside the fifthelectrically conductive surface.

[Item 10]

The slot antenna device of any of items 7 to 9, wherein,

the first electrically conductive member has an even number of slotsincluding the at least one slot, the even number of slots arranged in arow along a direction that the waveguide member extends;

the port is located in a center of the row of the even number of slots,as viewed from a direction perpendicular to the waveguide face; and

each of the even number of slots is open to the external space throughthe first electrically conductive surface.

[Item 11]

The slot antenna device of any of items 1 to 10, comprising a pluralityof ridge-shaped waveguide members including the waveguide member, theplurality of waveguide members being on the second electricallyconductive surface;

the first electrically conductive member has a plurality of slotsincluding the at least one slot, the plurality of slots being arrangedalong a direction which intersects a direction that the waveguide memberextends;

each of the plurality of waveguide members includes a plurality ofridges, such that ends of two adjacent ones of the plurality of ridgesoppose each other;

as viewed from a direction perpendicular to waveguide faces of theplurality of waveguide members, each of the plurality of slots islocated between the ends of two adjacent ones of the plurality ofridges; and

each of the plurality of slots is open to the external space through thefirst electrically conductive surface.

[Item 12]

A radar device comprising:

the slot antenna device of any of items 1 to 11; and

a microwave integrated circuit connected to the slot antenna device.

[Item 13]

A radar system comprising:

the radar device of item 12; and

a signal processing circuit connected to the microwave integratedcircuit of the radar device.

[Item 14]

A wireless communication system comprising:

the slot antenna device of any of items 1 to 11; and

a communication circuit connected to the slot antenna device.

A slot antenna device according to the present disclosure is usable inany technological field that makes use of an antenna. For example, theyare available to various applications where transmission/reception ofelectromagnetic waves of the gigahertz band or the terahertz band isperformed. In particular, they may be used in onboard radar systems,various types of monitoring systems, indoor positioning systems,wireless communication systems, etc., where downsizing is desired.

This application is based on Japanese Patent Applications No.2017-079997 filed on Apr. 13, 2017, the entire contents of which arehereby incorporated by reference.

What is claimed is:
 1. A slot antenna device, comprising: a firstelectrically conductive member having a first electrically conductivesurface on a front side and a second electrically conductive surface ona rear side, and having at least one slot extending from the firstelectrically conductive surface through to the second electricallyconductive surface; a second electrically conductive member on the rearside of the first electrically conductive member, the secondelectrically conductive member having a third electrically conductivesurface on the front side, the third electrically conductive surfaceopposing the second electrically conductive surface; a ridge-shapedwaveguide member on the second electrically conductive surface of thefirst electrically conductive member, the waveguide member having anelectrically-conductive waveguide face that opposes the thirdelectrically conductive surface and extending alongside the thirdelectrically conductive surface; and an artificial magnetic conductor onat least one of the second electrically conductive surface and the thirdelectrically conductive surface, the artificial magnetic conductorextending on both sides of the waveguide member, wherein, the thirdelectrically conductive surface, the waveguide face, and the artificialmagnetic conductor define a waveguide in a gap extending between thethird electrically conductive surface and the waveguide face; thewaveguide member includes a first ridge and a second ridge; one end ofthe first ridge and one end of the second ridge are opposed to eachother; as viewed from a direction perpendicular to the waveguide face,the at least one slot is located between the one end of the first ridgeand the one end of the second ridge; and the at least one slot is opento an external space through the first electrically conductive surface.2. The slot antenna device of claim 1, comprising a plurality ofridge-shaped waveguide members including the waveguide member, theplurality of waveguide members being on the second electricallyconductive surface; the first electrically conductive member has aplurality of slots including the at least one slot, the plurality ofslots being arranged along a direction which intersects a direction thatthe waveguide member extends; each of the plurality of waveguide membersincludes a plurality of ridges, such that ends of two adjacent ones ofthe plurality of ridges oppose each other; as viewed from a directionperpendicular to waveguide faces of the plurality of waveguide members,each of the plurality of slots is located between the ends of twoadjacent ones of the plurality of ridges; and each of the plurality ofslots is open to the external space through the first electricallyconductive surface.
 3. The slot antenna device of claim 1, wherein, thefirst electrically conductive member has a plurality of slots includingthe at least one slot, the plurality of slots being arranged along adirection that the waveguide member extends; the waveguide memberincludes a plurality of ridges including the first ridge and the secondridge; and as viewed from a direction perpendicular to the waveguideface, each of the plurality of slots is located between the opposingends of two adjacent ones of the plurality of ridges; and each of theplurality of slots is open to the external space through the firstelectrically conductive surface.
 4. The slot antenna device of claim 2,wherein, the first electrically conductive member has a plurality ofslots including the at least one slot, the plurality of slots beingarranged along a direction that the waveguide member extends; thewaveguide member includes a plurality of ridges including the firstridge and the second ridge; and as viewed from a direction perpendicularto the waveguide face, each of the plurality of slots is located betweenthe opposing ends of two adjacent ones of the plurality of ridges; andeach of the plurality of slots is open to the external space through thefirst electrically conductive surface.
 5. The slot antenna device ofclaim 1, wherein the second electrically conductive member further has:a fourth electrically conductive surface on the rear side; and a portextending from the third electrically conductive surface through to thefourth electrically conductive surface and opposing the waveguide faceof the waveguide member.
 6. The slot antenna device of claim 2, whereinthe second electrically conductive member further has: a fourthelectrically conductive surface on the rear side; and a port extendingfrom the third electrically conductive surface through to the fourthelectrically conductive surface and opposing the waveguide face of thewaveguide member.
 7. The slot antenna device of claim 3, wherein thesecond electrically conductive member further has: a fourth electricallyconductive surface on the rear side; and a port extending from the thirdelectrically conductive surface through to the fourth electricallyconductive surface and opposing the waveguide face of the waveguidemember.
 8. The slot antenna device of claim 4, wherein the secondelectrically conductive member further has: a fourth electricallyconductive surface on the rear side; and a port extending from the thirdelectrically conductive surface through to the fourth electricallyconductive surface and opposing the waveguide face of the waveguidemember.
 9. The slot antenna device of claim 5, further comprising: athird electrically conductive member having a fifth electricallyconductive surface on the front side, the fifth electrically conductivesurface opposing the fourth electrically conductive surface; and aridge-shaped second waveguide member on the fifth electricallyconductive surface, the second waveguide member having anelectrically-conductive waveguide face that opposes the fourthelectrically conductive surface and extending alongside the fourthelectrically conductive surface.
 10. The slot antenna device of claim 7,further comprising: a third electrically conductive member having afifth electrically conductive surface on the front side, the fifthelectrically conductive surface opposing the fourth electricallyconductive surface; and a ridge-shaped second waveguide member on thefifth electrically conductive surface, the second waveguide memberhaving an electrically-conductive waveguide face that opposes the fourthelectrically conductive surface and extending alongside the fourthelectrically conductive surface.
 11. The slot antenna device of claim 5,further comprising: a third electrically conductive member having afifth electrically conductive surface on the front side, the fifthelectrically conductive surface opposing the fourth electricallyconductive surface; and a ridge-shaped second waveguide member on thefourth electrically conductive surface, the second waveguide memberhaving an electrically-conductive waveguide face that opposes the fifthelectrically conductive surface and extending alongside the fifthelectrically conductive surface.
 12. The slot antenna device of claim 7,further comprising: a third electrically conductive member having afifth electrically conductive surface on the front side, the fifthelectrically conductive surface opposing the fourth electricallyconductive surface; and a ridge-shaped second waveguide member on thefourth electrically conductive surface, the second waveguide memberhaving an electrically-conductive waveguide face that opposes the fifthelectrically conductive surface and extending alongside the fifthelectrically conductive surface.
 13. The slot antenna device of claim 5,wherein, the first electrically conductive member has an even number ofslots including the at least one slot, the even number of slots arrangedin a row along a direction that the waveguide member extends; the portis located in a center of the row of the even number of slots, as viewedfrom a direction perpendicular to the waveguide face; and each of theeven number of slots is open to the external space through the firstelectrically conductive surface.
 14. The slot antenna device of claim 9,wherein, the first electrically conductive member has an even number ofslots including the at least one slot, the even number of slots arrangedin a row along a direction that the waveguide member extends; the portis located in a center of the row of the even number of slots, as viewedfrom a direction perpendicular to the waveguide face; and each of theeven number of slots is open to the external space through the firstelectrically conductive surface.
 15. The slot antenna device of claim 1,wherein, the first ridge and the second ridge have end faces that opposeeach other; and the end faces of the first ridge and the second ridgeare continuous with an inner wall surface of the slot without beingstepped.
 16. The slot antenna device of claim 9, wherein, the firstridge and the second ridge have end faces that oppose each other; andthe end faces of the first ridge and the second ridge are continuouswith an inner wall surface of the slot without being stepped.
 17. Theslot antenna device of claim 1, wherein the first electricallyconductive surface of the first electrically conductive member has ashape that defines at least one horn communicating with the at least oneslot.
 18. The slot antenna device of claim 8, wherein the firstelectrically conductive surface of the first electrically conductivemember has a shape that defines at least one horn communicating with theat least one slot.
 19. The slot antenna device of claim 1, wherein theat least one slot have an H shape that includes a pair of verticalportions and a lateral portion connecting between central portions ofthe pair of vertical portions.
 20. The slot antenna device of claim 18,wherein the at least one slot have an H shape that includes a pair ofvertical portions and a lateral portion connecting between centralportions of the pair of vertical portions.
 21. The slot antenna deviceof claim 8, wherein, the artificial magnetic conductor includes aplurality of electrically conductive rods on the second electricallyconductive surface; and each of the plurality of electrically conductiverods have a leading end opposed to the third electrically conductivesurface and a root connected to the second electrically conductivesurface.
 22. A radar device comprising: the slot antenna device of claim1; and a microwave integrated circuit connected to the slot antennadevice.
 23. A radar device comprising: the slot antenna device of claim4; and a microwave integrated circuit connected to the slot antennadevice.
 24. A radar device comprising: the slot antenna device of claim18; and a microwave integrated circuit connected to the slot antennadevice.